Would you be breaking her confidence if you talked to her counselor?
Could you try to convince her to bring it up with the counselor, and if she doesn't want to maybe you could ask her if she wouldn't mind you doing it?

i think it is always a difficult decision to know whether or not to try to help someone in this way. But anytime someone is restricting food intake it is considered 'disordered' eating. It would probably really help her if she had someone to talk to about it. She might really benefit from the help of her counselor or even a dietician to learn how to eat healthfully and to lose weight in a safe way.

Best of luck to you........let us know what happens.