You can't fix it, just be there for her. Accept her illness as you would any other illness in a friend, like high cholesterol or Asama, those don't get in the way of friendship but they do require changing some patterns, like if a friend of mine have high cholesterol, I'm not going to take her to a steak restaurant - that would be unfair and niether of us will have fun.
So, just go on being her friend and don't try to cure her. don't mention the eating disorder unless she does, and don't make any remarks on her looks even if she look wonderful, instead compliment her a lot about other parts in her life, like kindness, success at work, being talented and so on.
Also, I would probably avoid seeing her in restaurants, instead, go to the museum or park or places that are not food related.