Your friend needs help from responsible adults who understand her problem. Letting her parents know might be a first step but if her parents are critical, demanding and possibly abusive then look to a school or church adult who can help. Search the local mental health clinics, hospitals, women's support lines, help lines etc. until you get in touch with someone who is local to you and can help. Then go with your friend to whomever you both choose. Don't stop just because the first person you meet isn't the right one for her.
Much of today's music and media focuses on what's wrong with women and not what is wonderful about being a woman. Cutting can be an outward sign of an inner hurt that doesn't show because it is not the type of hurt that produces bruises and cuts. Emotional and verbal abuse can be behind it as can sexual abuse. There are better ways to deal with this than cutting to feel the pain.
Good luck!