She isn’t really doing it for herself but more for her mother and acceptance. I don’t think you have much to worry about….even if she loses a little she will gain it all back and more after she succumbs to eating normal again or less exercise.
If you say she doesn’t really want to….have a fun game at it….act like she is dieting for her mother’s sake…play it up with workout clothes on and acting like she is working out and eating less around her Mother and then you and her secretly have her stuff and eat a ton when she isn’t around her Mother….on two months time have her show up to her Mothers in some out grown workout clothes….sounds pretty fun to me. .
Just tell her... She knows you like her fat, doesn't she? Reassure her, be careful that she's still in good health. Be supportive. Her mother does not have to decide for her life.
