Talk to a counselor, therapist, or police officer and see if you can have her put in protective custody. There, she'll have access to the professional help she needs to get past this, and she'll have trained people to watch over her and keep her from succeeding in her suicide attempts.

It might sound extreme, and there's a chance that she'll hate you in the short term for doing this, but if you really love her and want to help her, that's the price you have to pay. Letting things continue as they are will do her no good at all.