I think my friend may be anorexic, what should I do?

My friend is beautiful, fit and skinny. But she is showing psychological signs of being an anorexic. She is aware consciously of how many calories are in all the foods she eats. She only allows herself 250 calories tops for one meal. Sometimes she will "forget" her lunch, or just skip meals. She works out, and still thinks she is fat. She compares herself to everyone, saying she is fatter than them. And she has tried to throw up before, but it doesn't work. She isn't like a stick, she is again at a beautiful weight. I am concerned. What should I do?