An eating disorder is just that, a disorder. You didn't give very much detail about this problem, but I think it's really important that your friend gets help. Eating disorders are a very serious addiction, and I think that's something that you need to realise here. I'm not an expert on this - but I have seen several friends suffer from eating disorders and none of them managed to overcome anything without the help of a professional. I'd really advise her to talk to a counsellor. Most schools provide free counselling, but if not, she can go to her doctor and ask about therapy sessions. Eating disorders start in the mind - they're not primarily physical disorders, and they often have a root course which can be uncovered in therapy sessions.
In the meantime - support her. Be there to listen to her and to help her, but don't force her to eat or to stop what she's doing - it won't work, and will most likely result in her increasing her behaviour out of stress. Good luck :)
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.:.Faut souffrir pour etre belle.:.
♥ hey there, delilah, what's it like in new york city?