Your mother has an unhealthy view of weight and its health implications. I've been there... my mom was bulemic and also I think in some ways anorexic. She was so tiny, every bone in her body showed. She ate less than 600 cals a day and threw up after dinner every night. (She's in treatment and is good now, despite some health issues she will live with the rest of her life due to the years of purging) She'd stand in the mirror in her underwear and slap her tiny little "pooch" on her belly - the only place on her body where there was any fat (which btw is the place where every woman in her family stores fat) and she'd say look at how fat and disgusting I am. I weighed 20 lbs more than she did and was one inch taller. I looked great and doctors said I was perfectly healthy. I was 110 and 5 feet tall. She made me feel I was so fat because I was fatter than she was. Now I really am overweight. I am struggling like crazy to lose it. My grandpa (her father who probably made her the way she was) bullies me about my weight (including yesterday during a visit). I'm trying so hard to lose it and just get healthy again. I thought I was so ugly when I was actually quite beautiful. Its so hard to set it aside.
When your mom hurts you this way, it is so hard to shelve it but you have to try. Your weight is beautifully healthy!!! You are probably gorgeous and curvacious and some women think feminine curves (breasts, hips, thighs) are a sign of overweight. Try to understand it is her insecurities about her own weight that she is pushing on you and there is nothing wrong with you!