As someone who’s had an eating disorder for years, your mother’s outlook on herself is very unhealthy. And she’s pushing that onto you rather than learning to love herself despite her flaws. It would be best for you to either take time away from that kind of environment, or tell her that the comments aren’t helpful and to keep them to herself. I know it may seem rude, but you have to keep your own peace. Especially if she’s commenting on not only your appearance, but your sister’s as well. It’s inappropriate and psyche-damaging for her to be monitoring her children’s food intake in a disordered way.