Wow! Yes, that is indeed the answer! Become a right BITCH!
Hmm, this will take me a while to plan out I suspect.
Let's see. Yes, I think I can understand your frustration about her annoying you when you're trying to study. That's one thing I agree with, you have to be firm with her. Maybe even lie.
I suggest, if you want to use Monday as solid study day well...well, well, well. If she asks you what you're up to on Mondays' tell her that you are going to be studying all day. Now if you want to help her with her studies, then tell her honestly when and where, and tell her to remember her stuff for studying. Maybe try and get there before her.
Now when she turns up, tell her that you can't talk as, I dunno, maybe a librarian already asked you to be quiet as you were talking too someone you happened to bump into. Oh yeah, hopefully I shouldn't have to tell you but make sure you're in the quiet section of the library, not the group section. And bring your mp3 player. As long as it's on low volume, that way you can study, and then you can help when she needs it, otherwise, you're listening to music.
Now if you don't want to help her, this is the lying, easier path, simply tell her that you're going to be in the library/your room all day, but instead stay in your room/go to the library. Make sure your mobile is switched off so you won't be disturbed. Then, when you talk to her later, simply say you changed your mind about where to study.
With regards to not being a bitch, don't get her nerves and constantly drop hints that she annoys the hell out of everyone. That's..just..horrible.
How close are you with this girl? You see what you could do is ask her out for coffee, tea, whatever’s your poison, and say to her that you want to discuss something with her. Now simply say to her that you'd like her to listen, and not speak until your done. Then proceed to say to her...whatever it is you need to say. Such as, you're more than willing to help her with studying, but she cannot talk as you find it hard to study when talking to people.
Also, try to tell her in a kind way that, while it's brilliant that she has something that interests her and that she's passionate about (re: Lara Croft) the fact that she talks about her constantly gets on peoples nerves. Ask her what other interests she has, such as the course that she's doing, and suggest that she talks about a wider range of subjects. Maybe she's into art, literature, philosophy, electronics, gush gooey romance films. Ask her about her other interests. If you find that you share some interests talk about them. If she is interested and knows about something that you're interested in but know little about, ask her too teach you a little bit about them.
With regards to interests don't lie! It's always plain when someone’s faking interest in something you're talking about and makes you very uncomfortable.
Right, I'm now going to get off my high horse. If there's anything else you'd like help with, don't hesitate to ask, unless you need help being a bitch, in which case you're on your own.