Self-cutting is a cry for help. My husband's niece was a cutter, and it turned out that she had been sexually abused by a friend of her older sister. I would encourage that person to get help. If you think that she would be resistant, speak to a teacher or counselor about getting help for her. They can keep it confidential that you talked with them. This isn't tattling; this is a very real, very serious problem that needs to be addressed as soon as possible.