Daughter’s Overeating Issue

My 12-year old daughter appears to have a flour/sugar addiction. Although the meals that she eats with me are mostly sugar/flour-free (I have been eating that way for almost a year), she eats only about 25% of her meals with me. All other times she is with her father whose diet consists of primarily processed foods, other relatives, or school. I have found her “sneaking” food and often accept sugary snacks from her dad, grandmother, and school friends while her protein/vegetable lunches come home uneaten. She also is about 20 lbs heavier than her peer group and has started to struggle with body image issues and comments from her peers. And finally, although she plays competitive soccer, she can’t keep up to her peers because of the extra weight. When I talk to her about it, I must come across as “preachy” because she tunes me out and/or becomes defensive. How do I help her through this without coming across as judgmental or condescending? I am trying to keep an emphasis on healthy body and self-care, but when she asks me if she is fat, I don’t know what to say. Growing up, I also had an overeating issue and there was significant emphasis put on body image. Our family values were around being smart and being thin. Now by avoiding the conversation all together, I am afraid that I am not giving her the support she needs. I also struggle to understand if this is a manual that I have for her. But on the other hand, how do I just sit by and watch her struggle?