Dr. Houtini,
I don't have a personal experience with eating disorders, but I believe they fall into the category of self-harm issues, emotionally. That I know a bit about, first-hand. The way to perhaps helping your friend, is to understand that she fears extreme boundary violations, emotionally. (Invalidation) She doesn't feel "safe" being herself; isn't comfortable in her own skin. (anxiety) She might feel her anger is "bad"... makes her a bad person... yet she can't help being angry, about whatever invalidation is still stuck in her stomach... indigestible; unprocessed... and so she also feels --
helpless and powerless and the one thing she can control is her own body. Complicating that, is probably an association of food with comfort, filling her needs (tho' in reality those needs are emotional - not hunger; the food is a substitute)... and so she is compelled, in the midst of all this emotional push-pull confusion, to purge also.... which keeps the cycle (feedback loop) going round in circles with no apparent way out.
There is always a way out -- but those of us caught in these are too close to them, to see them. We believe that "this is just the way we are" -- WHO we are and we can't stop, without stopping being ourselves. It almost always takes a compassionate friend (or three) or therapist to help us see those doors out of the loop - in a present moment - repeatedly, until we learn to start seeing these and walking through the door, ourselves. Because of the identity-association with the behaviors, it's a traumatic fear to comtemplate letting go of the feedback loop... and becoming "someone else".
My advice is to help her feel safe, recognized and seen/heard, to gently (and without criticism) show her the doors (choices) in front of her if you notice she's running the maze of her feedback loop... and try to slowly persuade her that she's not a bad person, she's competent, confident, and has immense control over her choices - internal and external. Help her see/learn and feel boundaries. Listen for her code-speak about her feelings, help her learn other ways to express her feelings verbally -- and not through abusing her body. Let her know you "hear" her (and her feelings) loud & clear -- the thirst for that kind of validation seems almost insatiable at first. But with experience of boundaries, it normalizes over time.
All easier said, than done. Good on you for wanting to help her and best of luck!