I have a high regard for friendship and your desire to help your friend. However, she is in need of professional help, and your job can be to encourage her to stay connected to her counselor. The most direct way is for you to talk to your school counselor about what you’ve been told and what you notice. This is important because her condition is now affecting you, and the counselor can help both of you. You can also offer to go with your friend to her counselor, or write out your concerns and ask her to share your list with her therapist.
There are also good blogs with information on dancing and eating disorders you can pass on to your friend (like this one http://www.dancespirit.com/starving_for_perfection-2326081076.html), or make her aware of the eating disorder forum here at Psych Central. Here is another resource on cutting she may find useful.