Hi Mike,
Thanks for your letter and for your trust! I think it's a really important and serious problem so i try to be useful.
At first, you have to understand that at girls the weight is a big taboo. I think it is almost anorexia so you must be calmed and polite.
Of course the best thing to do is sit down and talk with her. You have to try explain that she is beautiful and the weight doesn't matter. She is wonderful,tiny and totally likeable. You are her best friend so she is going to obey.
As i said it's a really taboo so don't tell about it anybody! Anorexia at a girl is really personal. If you aren't enough to help try to make an appointment to a psychologist.
Good luck,
(A neved)