I'm going out on a limb and assuming that your little munchkins are not in fact powergaming munchkins?
Forget the rules and make your daughter a cat. Not a cat person, but a cat.
Best race to use? Leopard.
It's a CR 3 medium animal.
Adapting the rules for animal advancement to animal de-advancement you could end up with a small CR1 Animal pretty easily, which should be her first level.
This thing has Improved grab, pounce, rake 1d3+1, Low-light vision, scent, and good racial bonuses to jump, hide, move silently, balance and climb.
The character will play a bit like a combination rouge/scout/ranger/monk.
For advancement, 1 HD every level, remembering size change back to Medium at a Leopard’s normal HD, or take levels in Monk (which will max the characters strengths of mobility and damage, just adapt the normal monk’s damage dice increase to increase the leopard’s by the same number of steps, whilst also providing some way to overcome DR).
Ensure that she acquires equipment. Amulet of mighty fists, and get her some exotic barding if she isn’t going the Monk route. Or, if you don’t like the idea of cats with magic items? Go Vow of Poverty from BoED.
Probably replace a leopard’s intelligence of 2(-4) with –(0), as with a construct’s Con. – Disallow spellcasting/knowledge of anything but nature etc, but without crippling the character’s ability to get movement related skills that scale at similar levels to normal characters.
Because animals get mediocre benefits for increasing HD by 1 (unless they change a size category) compared to a player increasing level by 1 (animals get 1d8 HD, 0.75 BaB and 2 good saves, compared to a Monk that gets 1d8, 0.75, 3 good saves and heaps of abilities) you will need to find some way to buff the character if (and only if) they choose animal HD instead of Monk levels. Probably the easiest is to use the Druid animal companion abilities (str/dex, natural armour, abilities such as evasion). Obviously, do not give out the bonus HD, and ignore bonus tricks. You could then also allow the character to give up their additional animal HD to become a more powerful Creature: leopard – lion – tiger – dire lion – dire tiger, following the druid animal companion rules.
You might need to change some of this depending on whether she is more or less powerful than other characters. I’ve never actually done this, so no guarentees re: balance. I think if anything, it will be underpowered – it’s basically just a druid’s animal companion, that gains 1 HD/level instead of 2/3 HD/level, but can’t get the +6 level from beastmaster/that feat (although it will get character type base stats instead of the 11/10/11/10/11/10 that I think animal companions get. So for starting stats, roll the dice normally, and add the leopards total stat, then subtract 11 or 10). But then you don’t get a druid riding on your back summoning stuff. Druids already can choose to put all their magical equipment on the animal companion.
Hope this helps.
Edit: I forgot to mention, if you are having your character change between types of cats as they level up, there might be a bit of inconsistency with skills. Some of the cats have (or lack) skills they might be expected to have. I think some can't jump, or suck at move silently/hide in shadows. I would advise keeping the Leopard's racial bonuses and starting skills and just having your daughter take more ranks in appropriate skills each level up). Keeps things simpler.