Okay kiddo's, self mutilation or self injury is to be taken seriously. Show your friend you care about her, talk to her, be there for her. She does NOT need parenting. It doesnt matter how deep of shallow she cuts, the fact that she cuts is bad enough. By depth you cannot see how severe the emotional problems are.
Even kids who say "Hi, my name is .... and I cut myself, look!" do have a serious problem, though those handle a different approach. I am not talking about those self injurers.
Its not weird that you dont really know what to do, lots professional people still don't know how to deal with it. If you have any questions or whatever, PM me or post here, I've cut myself for over years, I think I can answer alot of your questions.