It sounds worthwhile to get out of that situation. Maybe you're not as stuck as you think?

I'm sorry you're stuck with such a horrible person, do what you can to get out of that situation, and I hope goes well for you.

That's not good for your mental health. I hope you can find a way to do something about it!

What sort of roommate? Are you renting an apartment, or is it a college dorm? Because if it's the later, you can probably get a note from a doctor (a psychiatrist would be best) stating that you need to be relocated for mental health reasons. If you have preexisting mental issues, you should have it easier, especially if you have a disability aid form on file. Legally they have to make reasonable accommodation to students, and a change of room or roommate should fall under reasonable accommodation. Another option if it is campus/college funded dorm, is that any college or university that receives federal funding is just as legally bound to stopping and punishing harassment as other school groups. If it's the first... It may be worth the trouble to tell her to either knock it off or you'll buy out your part of the lease and leave. Or if that isn't an option, asking some friends if they mind you couch surfing and then leaving with doing anything in regards to the lease or other bills. Hope something helps you get out of this situation- it sounds like it could cause some major medical issues. (Also, again, not a lawyer, just giving advice as someone who was severely harassed at several points in their school career.)