(((((((((Deki88))))))))))))))
I'm sorry you're struggling with your own ED, and that your sister is struggling with her own.
Have you read any books on the topic? There are a lot of good ones out there that discuss helping someone with an ED. Otherwise, do you/her see any sort of counsellor/therapist or some sort of professional? It sounds like having that sort of help would be beneficial to you both. I know its hard dealing with our own problems and seeing someone we love struggling and not knowing how to help. When I was faced with this, I tried to remain open and let my sister know that I was willing to listen if she ever wanted to talk. Don't engage in a power-struggle with her for control, because it is a form of controlling ones life, by controlling how much one eats.
I hope that helps.