Also, you live in a liberal democracy with more of a social safety net than we have. It is very likely that your roommate needs a social worker, and can possibly get some kind of disability allowance for mental illness. Maybe a call to a domestic violence shelter would result in a referral to appropriate resources. Surely there is some kind of local government mental health council.
Next, find out the rules for evicting roommates in your location. Generally, you have to go to court for these things, and it can take quite some time. (While I’m sure you can lock up your half of the dishes and let her use her own, dirty half of the dishes, the law in NYC, at least, strongly frowns upon changing the locks to the apartment, putting a lock on the bathroom, and other such dirty tricks.) Find out the legal procedure, which probably begins with asking your roommate, in writing, to leave within 30 days. This gives you some documentation for when/if you begin legal proceedings.
Finally: What’s the worst that would happen if you just walked away? You lose your deposit, you damage your credit, you have a hard time renting another apartment (unless you become someone else’s roommate), the landlord could keep coming after you for rent? I’m not saying these aren’t pretty terrible consequences. They are. But it’s helpful to put your finger on these consequences — and the actual probability of each one happening — so you are not afraid of some giant, nebulous bogeyman of badness that seems as though it would last forever and take over your whole life. Even very bad consequences are generally contained, both in terms of time and in terms of which segments of your life they affect. Even if ALL of the above happened, it wouldn’t affect your health, your schoolwork, or your love life, for instance. It would be terribly unfair if your credit were damaged due to no fault of your own, but that doesn’t last forever, either.
The other thing that this reminds me is, well … helping is really hard. Much harder than you would ever think. I mean, maybe you can go donate some supplies to a school and the kids will send you a thank-you note in crayon and you’re in and out and you feel great. Maybe. But most kinds of helping are much, much harder, and you just end up feeling ambivalent: good that you tried, but skeptical that you tried in the best way, and doubtful that the problem will get much better, ever. My friend Janice Erlbaum wrote a memoir about how even the most heartfelt attempts at helping can go very, very wrong.
I once went on a first date with a guidance counselor at an at-risk high school, and I commented on the low success rate for helping in general. I said, “It’s like if you actually help 25% of cases, you’re amazing.” He said, “Oh god, I wish it were 25%. Maybe 5%?” He then told me a story about advocating to get one of his students out of jail on parole. Thanks to his help, the student was back in school, where he then stabbed someone.
In contrast, helping wealthy people who are already really together is not only fantastically more lucrative, but much, much easier. Rewards in life are not doled out in response to mere effort. It greatly depends on where you allocate those efforts in the first place.
Personally, I have found that helping the saddest cases is not for me. I would rather work with moderately to highly functional people and then maybe donate money to causes that help the sorriest cases. Or, ideally, I would like the government to send out social workers. I do not want to personally be in the business of helping people who damage themselves, say they’re going to do things and then never (never!) do them, and can’t wash a damn dish. You don’t have to either. At least not for a mere acquaintance. Probably not for anyone but your own children. Your own mental health demands that this end.