Isis: Prioritizing your studies is important, but you gotta take care of your body as well. Don't feel guilty about doing something that's ultimately good for your health. But if you do need to get something done and you need sleep as well, try taking naps! That would really help you get even a little bit of rest so you can have enough energy and alertness to do your business. Here's an infographic of the length of naps you should take to maximize productivity:
Isis: There's no other way to go about this than to give it to her straight: tell her you feel bothered by her mess. Since you live together it's important that each of you feel comfortable in your shared living space. Tell her, as nicely and politely as you can, that you won't tolerate her messiness. Try to reason with her and compromise with her if it really bothers you.
Ana: Tell it to her straight. It's her mess, yes, but you guys live together and no one wants to live in a mess. You can also try cleaning up her things with her. You can do the work together and talk to her there about how her mess bothers you. (also, doesn't your roommate feel guilty or ashamed that you're the one that's cleaning up after her???? gurrrrl.)