My 13 year old daughter told me on the way to her teen mission trip that she cuts. She promised her you...
All you can do is talk regularly to her about it & how she is feeling. Well done for not reacting. I wouldn't take her knife away as she may then move on to razor blades etc. If she wants something to use, she will find it regardless of you. I think it's a great idea for her to have a support buddy. You will not have to pay for counselling for her if you have a word with your GP, as they will refer her. You have responded to her in a very supportive way. Good luck.