Accoording to what she has told my friend she was in hospital a lot of last year. And she told me sha has had problems since she was 11. I've decided there is nothing else I can do. Her flatmates have already told the hall warden (head of accomodation) and asked them to do something but as far as I know they just came round to the flats handing out ed leaflets and counselling leaflets to everyone.
Her BMI is probably 19-21. I have kinda decided to wash my hands of it unless she approaches me with a different attitude.
Thanks for the comments, made me feel less insane!