Compared to 4e...
3.PF do not have nearly as much active battlefield control, and it’s all magic
Both Pathfinder and 3.5 before it lack 4e’s emphasis on positioning in combat. There are very, very few abilities that push or pull enemies, and basically all “zones” are magical in nature (though they are frequently very potent).
Battlefield control is typically done best by Wizards and Druids. Clerics can be pretty good at it too, and have a more martial bent. For Pathfinder-specific classes, the Summoner can be quite solid at it as well. Witches tend to be more about debuffing, targeting foes directly, and the Magus is largely about direct-damage.
The only real mundane options are Tripping, and Grappling.
I’m ignoring Bull Rush (Barbarians are just so obviously better, plus it just doesn’t help much in 3.PF), Disarm (locked gauntlets shut that down too hard), and Sunder (hard to do, destroys potentially-valuable loot) as tactics that aren’t worth even considering.
Tripping was a fairly solid tactic in 3.5, though it still paled in comparison to what magic could do. Pathfinder nerfed it drastically, but it’s still just about the best option available to mundane characters.
The typical trip-lockdown build focuses on attacks of opportunity and reach. The idea is to stand in the enemies’ way, with too large a threatened area to go around, so that they have to take an Attack of Opportunity from you. You then Trip on the Attack of Opportunity, and success means you get another attack to try for some damage too. Getting up on their next turn provokes another Attack of Opportunity (you cannot trip them again, however), and burns a Move action, so they either have to stay put or use their Standard to move, leaving them no actions with which to do something. This is a pretty effective tactic, so long as you can actually bar their way and succeed on the trip check.
Because Attacks of Opportunity are so important, Combat Reflexes (and reasonable Dex) is a must. Because you need to use tripping a lot, you obviously need Improved Trip, which usually means Combat Expertise (and Int 13). In 3.5, that would be enough. In Pathfinder, you also need Greater Trip, and you’ll burn a ton of Attacks of Opportunity (i.e. you’ll need a lot more Dex) since Greater Trip’s attack requires an AoO unlike 3.5-Improved Trip’s completely-free attack.
Grappling relies on Improved Grapple (and thus requires Improved Unarmed Strike), which are easy for a Monk, but is impossible to use on creatures more than two size categories larger than you and spellcasters can easily avoid it once they have 4th-level spells thanks to freedom of movement and dimension door. As a tactic, at best it only stops one enemy, and a lot of monsters are just going to be much better at it than you are. And at high levels, any Combat Manuever is very difficult to use against anyone, due to how CMB and CMD are calculated in Pathfinder.
3.PF are not balanced, and the Monk class particularly so
Another thing you’ll have to get used to, coming from 4e, is that neither 3.5 nor Pathfinder are at all balanced, and magic dominates everything. The Monk class, in particular, is very weak (see “Optimizing a D&D 3.5 Monk” and “Does Pathfinder significantly fix known problems with the Monk class?” for more details). That fact basically sets the tenor of this entire answer.
3.PF do not let you “catch up” if you start a magic career late
Particularly Pathfinder. Unfortunately, a lot of Pathfinder’s changes, relative to 3.5, are geared towards disincentivizing multiclassing. Paizo felt that 3.5 encouraged far too much multiclassing. In 3.5, you could do, say, Fighter 2/Barbarian 2/Ranger 2/Horizon Walker 6 (the so-called “Horizon Tripper” build), which is pretty solid at mostly-mundane battlefield control, but Paizo really disliked that kind of crazy mish-mash of classes. Thus, you are strongly encouraged by the rules of Pathfinder to stay in one class, and most prestige classes are fairly poor. Ultimately, though, it’s difficult, even in 3.5, to start a magic career late. Pathfinder heightened that.
Getting away from Monk
Basically, to sum up, to get good battlefield control you need magic, but multiclassing into a magical class late tends to work poorly. The Monk class is very poor, though, so it may be for the best, particularly if there aren’t a lot of levels wasted in Monk.
Cleric class: an option, but best as a replacement
So multiclassing into Cleric now is not a great idea. It can work OK if you have only a few (say, 3 at the most) Monk levels, but literally every Monk level you have detracts from your overall power as a Cleric.
Instead, using just the Cleric class to make a “monkish” character tends to work much better than actually using the Monk class. Just take Improved Unarmed Strike, and go to town. The Monk’s Belt item can get you Wis to AC, too.
A mix is best done with only a single level of Monk; this grants you a couple of feats, Wis to AC without/before you can afford a Monk’s Belt, and some may feel better about calling themselves a “monk” if the Monk class is to be found on their character sheet. Ultimately, I’d strongly suggest not doing so. In 3.5, the Sacred Fist prestige class from Complete Divine makes a single level of Monk (for early Stunning Fist) a much more valuable option, but Pathfinder doesn’t have that.
Single-level Cleric dip: very useful in general, but not particularly here
Finally, note that Cleric, in particular, makes an excellent single-level dip for almost anyone. This costs more in Pathfinder than it did in 3.5, and 3.5 also had some notable options (Cloistered Cleric, divine feats, devotion feats especially Travel Devotion) that made it better. Still, you can get a lot of stuff from a single level by picking your Domains right, and the Channeling feature is often used as a requirement for things; some of those may be useful. So anyone could consider a level in Cleric. But so far as I know it does not directly help battlefield control.
Fighter or Barbarian
Both of these classes are much better at the best form of mundane battlefield control, trip-lockdown, than is the Monk, as I’ll get to in a minute. Unfortunately, switching here is awkward; most of the reasons that Fighters or Barbarians are better come from more efficient use of ability scores, but you can only take advantage of that as a Monk/Fighter or Monk/Barbarian if you ignore some or all of your Monk features, which then begs the question of why you have them in the first place. Barbarian has the added problem of alignment conflict; you can change alignment, but it may be difficult to do so naturally and fluidly within the narrative.
Still, if she has no more than 4 Monk levels, she could benefit from these classes simply because they have full BAB. That means she only lost one BAB from taking Monk, and that will help with some of the problems she could face.
I’m not going into more detail because then this would turn into an answer about Fighter or Barbarian, not the Monk.
Unfortunately, Monk class features give her no particular skill at battlefield control
Nothing about “having levels in the Monk class” makes her particularly good at doing this. She has some ability at Combat Maneuvers, and Tripping is a fairly good way to achieve battlefield control,1 but the myriad problems of the Monk class itself prevent her from doing so as effectively as, say, a Barbarian or Fighter.
Alternatively, she could try Grappling. Monks do have some things that improve Grappling, at least so long as she takes the correct archetype, but Grappling itself is not a great tactic.
Low AC and HP
First, she is not good at handling the attention she would draw to herself as a battlefield controller. Battlefield control is a major problem for the enemy, and something they want to get rid of. When battlefield control is coming from a Barbarian or Fighter, that represents a somewhat difficult-to-remove threat. Those classes have lots of HP and high AC; she does not. Magic makes them suffer, and her high saves and touch AC provide some protection from that, but not enough.2 Meanwhile physical bruisers will force her to retreat, or die, quickly, while they’ll have a hard time contending with a Barbarian or Fighter.
The reasons for this are simple: she has a d8 HD, and cannot wear armor. She gets Wis to AC, but considering your typical heavy armor is giving between +6 and +9 AC before magic even enters into the equation, that’s a lot of Wisdom she’d need to keep up. Realistically, it’ll take both Dex and Wis, which is extremely expensive. Meanwhile, if she does have a lot of Wisdom (or a decent chunk of both Dex and Wis), then her Constitution suffers – and then her HP is looking very, very low compared to the d10 or d12 HD of Fighters and Barbarians, who, let’s not forget, also have good Constitution most of the time because they don’t need more than a little Dex, and don’t need Wis for much of anything.
Monk Weapons are bad for this
She also suffers since no Monk weapon is particularly good at trip-lockdown. The gold standard here is the Guisarme, since it has Reach and Trip, which Monks don’t have proficiency in, and none of the Monk weapons have that combination of Reach and Trip unless she expends Exotic Weapon Proficiency in the Kusari-Gama or Double-chained Kama. But she’ll probably have to do that, because she really does need Reach to do trip-lockdown. In fact, she needs Reach and then she also needs to figure out a way to get size increases, if she can (Pathfinder makes this quite difficult compared to 3.5, sadly).
The alternative, Grapple, is better, but not great. Grapple doesn’t often get to use Reach, so she won’t be worse off in that regard, and Unarmed Strike’s damage is used for Grappling no matter what she does. Unfortunately, Grappling is just a weaker tactic all around.
Class Features just don’t help tripping
Furthermore, her class features do not help her overly much with trip-lockdown-style battlefield control. Because of everyone else’s speed limits, it’s rare that she’ll need to actually use her Fast Movement to reposition. Abundant step is nice, but extremely limited. Since she desperately needs Reach, you aren’t using her Unarmed Strike damage. And so on and so forth.
Monk class features do improve Grappling. It’s just not a very good tactic.
Difficulty qualifying for feats
Monks in Pathfinder still have medium BAB. While they do get to treat their BAB as full for the purposes of Flurry of Blows and Combat Maneuvers, they don’t get to do so for the purposes of feat requirements, most notably the BAB +6 requirement of Greater Trip. This is a very serious problem that will plague the Monk for her entire career.
Feats aren’t a great solution to core problems anyway
There are a number of feats, Monk-specific or at least that a Monk can easily qualify for, that help out. mxyzplk lists several, for example, and there are more. These can definitely help. The problem is, and the reason I don’t list them out, is simply because they don’t do enough, or put another way, you don’t get enough feats. Feats are an extremely valuable resource, and you only get a limited number of them. Burning multiple feats to try to fix the various problems is playing a game of catch-up that you’ll never win.
It’s probably worth doing if you’re sticking it out as a Monk, but ultimately it’s not enough to make my advice anything other than “minimize the amount of Monk in your game.”
Multiple Ability Dependency
As already pointed out, she has small HD and a strong need for Wisdom that other classes lack. She needs at least 13 Int for Combat Expertise, so you cannot get extra ability points by dumping that. Tripping relies on Strength, but she can’t ignore Dex either because her Wis isn’t actually going to make up for your lack of armor. As a result, her Trip checks are lower, her HP is dramatically less, and her armored AC is very poor. This makes her very bad at controlling the battlefield and protecting, well, anything. It actually is a major reason why the Monk class is one of the weakest in 3.PF.
This affects Grappling as much as it does Trip. She’ll possibly dump Dex since you lose it while Grappling anyway, and she doesn’t need Combat Expertise so she doesn’t need so much Int, but that still leaves a very difficult split between Str, Con, and Wis. Compared to a Barbarian who can use just Str and Con, and gets bonuses to those, and has much larger HD to begin with... that doesn’t work out very well.
1 For a mundane character, anyway. Compared to the magical battlefield control that’s available, it’s pretty pathetic.
2 Note that smart spellcasters can do things that entirely ignore your saves or touch AC. Even if it’s just summoning up something bigger or nastier, or casting spells on themselves or their allies to make them bigger and nastier.