That sounds painful...

Does she listen to you? Can you remind her that back injuries require rest and gentle movement to heal? If she enjoys exercise and wants to continue exercising once she is healthier and eating enough again, it's important that she take care of herself now, or some physical activities may become much harder.

One thing (this may be totally off base, or not)--Are you sure she is angry at you for eating for her? She may be more frightened at having "lost control" than really angry. Or perhaps frightened and angry, both.

I don't know you, but you seem to have a lot of strength. All of you together have gotten through a lot of stuff. Sooner or later, that strength will come through for you and things will get better.