This is true. Even if it never becomes a full-blown eating disorder.NOTHING GOOD CAN COME FROM THINKING LIKE THIS. Period.
If your daughter's health is affected, or it becomes apparent that disordered eating (such as binging) is behind her weight gain, then someone who cares about her should step in. However, if that happens, it might be better for everyone involved if another relative took care of it. (I'm just going by what's been posted on this site. I don't mean to be presumptuous or act like I know you well, Frau.)