It's an interesting question with a lot of potential depth, but the number one thing to do here is exactly what you did: Provide feedback afterwards. Having a bad experience GM:ing is OK and can help you to be a better GM, but only if you can ventilate what happened with someone. You gave her that opportunity and it will probably help her a lot in the future.
But the question was about what you can do during gameplay.
The following are all things that I have done at one point or another. You can do these yourself, but getting one or more players in on it helps.
Provide direct feedback
First, flash a carrot whenever the GM does something you enjoy. If there is something the GM provides more or better detail for, say that you liked it as soon as possible. To stop risking the game turning into a GM discussion you should state your actions directly after that. Let's say, for instance, that the GM describes a room in a bit more detail. You could go:
"Nice description. I like that. Anyway, I start going through the dresser since there is where I would have hidden the book."
Be transparent
The above sentence also serves to tell the GM how your character thinks. This is also important. Try to narrate the thought process of your character a bit; make yourself more transparent. Voice the motivation of your actions whenever practical. And naturally, don't overdo it.
Ask for more information
Whenever there is detail lacking, ask the GM to provide it. Help the GM to flesh things out if they're having problems with it.
"You arrive at a castle. There are two guards outside. Do you want to try and get in?"
The first thing to do here is to ask for more information. If the GM has a hard time coming up with descriptions or doesn't know what to include, ask more specific questions and provide options. Is the castle large or small? Is there a moat and a drawbridge? Are the gates open to allow for traffic or closed to prevent entry? Are the guards stopping people from entering or are they there to provide security in case of an incident?
The options let the GM know what kind of information you're after. This is key to getting good descriptions.
Ask for motivation
GM: "Do you want to inspect the rock?"
P1: "I'm not really interested in plain rocks. Is there something special that draws my eye to this rock?"
What makes railroading bad for me is when things are dictated for my character without any good reason. If the GM points out something that's out of the ordinary I get the hint and investigate it, but if the GM just decides I investigate something it feels forced. Pointing out something that grabs my attention and giving me a reason for why I find it interesting gives me the feeling of choice, even though I know that it's a plot device.
You can encourage your GM to give you reasons for why the things should be investigated by asking for the motivation behind it and telling them that it's not normally something you would investigate. When the GM starts getting into the habit of providing a reason, the adventure begins to feel a bit less railroaded.
Ask for certain scenes
In a campaign, we were stranded on an island. Our GM wanted to streamline things and fast-forward to the point where we were rescued. Normally this might have been a good move, but there were a lot of things in motion in the group at the moment and we basically stopped him and told him that we needed to RP a bit between ourselves on the island to work through some of the stuff that had just happened.
If you feel that there is a need for interaction between the PCs or there is some other scene you want to do, don't be afraid to tell the GM. As exampled by the situation in our game, this holds true no matter the experience of the GM and it can really help a new GM to learn what kind of scenes to throw in.
Hijack the session
You can be a bit aggressive and basically hijack the action for a little bit if needed. Perhaps you've just finished up a fight, the GM tells you a note found on one of the bodies points you to a certain location and that you go there.
GM: "You're at the entrance of the dungeon. Cale is held prisoner in there and you need to free him."
P1: "Hey Linda, I thought you said you were a bad rider. We made it here pretty fast though."
P2: "I never said I was bad at it, I just said I didn't like it. You see, when I was younger..."
You can also rewind the action a bit:
GM: "You're at the entrance of the dungeon. Cale is held prisoner in there and you need to free him."
P1: "On one of our breaks on the way I take Linda aside. Hey Linda, you look a fair bit grumpier than usual. Is there something going on?"
P2: "It's really nothing, don't worry about it. It's just all this riding that's getting to me. You see, when I was younger..."
The last examples might not be so much asking for scenes as simple doing them anyway, but as long as it's handled well it shouldn't be a problem. It can be a great way to engage a bored player and let them have some screentime.
And while all examples here have been interaction between players, you can just as easily force a scene anywhere.
GM: "The street urchin gives you a map with the location of the dungeon you need to go to. You're at the entrance of the dungeon. Cale is held prisoner in there and you need to free him."
P1: "Before we leave the city I visit a blacksmith. I need to purchase new arrowheads. Do you guys wanna come with me or do you have other stuff you need to do? If you do, we could meet up at..."
Now you've given the other players some free time to do things they want to do. It might not always work well, but it is at least something to help fend off the boredom.
And yes, this can all go horribly wrong if the GM feels like they've been ousted. Make sure you don't do it too often, make sure it's not too blatant and make sure the GM is still in charge of what happens.
In case of emergency; push the red button
Should all else fail and noone seems to be enjoying themselves there are basically two things to do:
Endure it. If it's just a one-time game you can all have a coffee afterwards and talk about how awful it was. It's actually good to be bored once in a while to have something to remind you of how awesome your other sessions are.
Stop the action and tell the GM that this isn't working. Tell them why, tell them how it can be helped, tell them it's OK to not be perfect and tell them that not all GM styles work with all player styles. Discuss how to continue and what you can do to help the GM.
In truth, most of the time I go for option 1 which is the safe way, but option 2 can be a great opportunity for the GM to grow and learn.
Not all sessions and GMs can be saved, but even a trainwreck of a game can be used to help the next one. I've had sessions, both as GM and player, where we've stopped playing because people weren't enjoying themselves. The key to everything, no matter how it turns out, is constructive criticism. No blaming, no pointing fingers. A GM that's struggling and not making it needs help and support. Yes, the flaws need to be pointed out, but always - no matter how bad the GM - encourage and support and never act like you're better.