Let me ask u a serious question. Were yall ever JUST friends or did yall just kinda...fall together? Cause if its the latter then yall fell into a trap from the get go. Its levels and forms of intimacy. That lady is sick. Last thing she needs is a boyfriend and the last thing u need is a sick girlfriend. If u care about her and urself let this girlfriend shit go, try to be her friend and make ur friend get the help they need. Dont be harsh or judgemental treat her like u would anyone else u care for platonically who is ill and like while showing urself all due love.
Dont baby her, dont go backwards. This shit wont get better overnight. The best u can do is get in her ass every time she start slipping and file them papers if necessary. If u wanna have her in ur life these are the least of the boundaries i would set. She needs serious help and is very much not nearly ready to be with anyone. But she do sound like she could use a friend. Thats entirely up to u though and its not gonna be an easy ride in all likelihood.