I agree with the other posters that your girlfriend needs help from a professional.
I'd like to point out that self-harming results from a depressive illness, and thus she needs to be treated for depression. This can be done with the help of drugs, but as a nutritional psychologist I suggest that this should be done by nutritional means.
Ask her parents to read:
Depression: a Disease of Energy Production
and have them discuss thid with a doctor familiar with nutritional medicine to treat her condition.