It sounds like your a great friend sticking with her, and being able to relate to her. The thing is...if your fears are right, she will get worse, and probably make a suicide attempt. Either that'll kick start something in her to change, or...it wont.
Continue to be there for her, but if she ultimately decides she's had enough, it's not your fault and you shouldn't feel guilty.
If you can't hack life, then move along.