I'd really try and encourage her to seek some help. It doesn't matter whether it's just a little bit or a lot, it's still cutting and it's still a sign of some problems or stuff going on with her that she's obviously not handling very well. Try and see if you can get her to go and see her GP or a counsellor, but don't force the issue... you can't make her get help, she has to want it for herself. Try and be there for her too, but don't judge, and make sure you are supported yourself. It can be tough supporting a friend.