She cuts herself, she's overweight, and she's promiscuous? Serious self esteem and self worth issues at play!!
You need to help her love herself and feel good about herself. Maybe try and convince her to take a break from dating for a while to focus on herself which could also improve any future relationships she may have. Maybe the two of you could learn a new skill together, or take a class, or do something she might be interested in. Help her grow as a person, make her feel like she has worth, help her develop self respect.
Or if you don't care to do any of that, then either accept her for how she is or stop hanging out with her.