You say she’s estranged from her family, but once you try to commit suicide, you’ve crossed a line. Normally, it would be a violation of her boundaries to get in touch with her parents against her will, but when there’s an attempt on a human life (anyone’s), she’s already broken the social contract that protects those kinds of boundaries. Sure, maybe you try to talk to her about why she doesn’t talk to her parents. Maybe she has some other family members she likes more. But this is really the sort of thing that families are for (not roommates).
In terms of the shitty roommate stuff, you can always pull the classic move of putting her dirty dishes on her bed. (Maybe in a dishpan, to be nice.) You can put a lock on “your” kitchen cabinets, where you keep your clean dishes (and your food, for that matter). Or you could try to avoid conflict by spending $1.99 on some paper plates. You could mess with her a bit by keeping your crackers in the tampon box and your tampons in the crackers box, so at least she’ll have a harder time stealing your food. Mix a tremendous quantity of hot sauce into the Vegemite. (Hot sauce can’t actually hurt anyone. If she complains, she’ll be admitting stealing your food!) But of course small acts of mischief wonâ€™t solve the real problem.
But yes, you need to ask her to leave. I wrote a column once about helpful ways to phrase things in which I suggested, “It’s not possible.” This phrase avoids having to talk about feelings (“I feel like you don’t respect my contributions…” — it’s too arguable.) Saying, “It’s not possible for us to continue living together because I don’t have the money to cover for you” is just a fact.
That said, young people like yourself often do not realize just how much older people are ready and willing to help. Not just faraway advice columnists! It sounds like your own parents aren’t that helpful. But you’re both students, right? You have a dean (or whatever it’s called in Australia) and so does she. Universities are EXTREMELY interested in getting involved in students’ problems before those students commit suicide. Maybe you or she could be moved into university housing. Maybe there’s some kind of emergency assistance available. You need to put out a call for help ASAP to your dean, her dean, the campus health service, and anyone else at the university who may be helpful. I promise you that there is someone at your university who would be horrified to hear that you are dealing with this all by yourself. Universities are used to acting in loco parentis.