i once dated this girl who used to be an alcoholic, did her big share of hard drugs, and really scarred her life
in the end i realized i was with her because i thought i could help her... and she had a hot ass.
but my point is that you might do it because of mercy not because of affection.
many guys tend to do it, we like being protective.
it would seem unfair though to discard her right away, i mean truly maybe nobody has given her a chance
if i was you, i would:
-confront her, tell her that you care about her and that you wanna start something, but you need her to change
-no more weird male friends stalking (its probably her fault)
-no hard drugs, that just takes her closer to insanity.
-she should try to leave whatever crap influences she had.
mainly a complete reset of her lifestyle
if she is not willing then tell her to go fuck herself
you see she might really in trouble, trying to find shelter and stable-ness, or she might just be a crazy bitch