I am opinionated about doctors, sorry about this but I will go there first. I think any physician in this day of kids having a problem with weight would jump right on it. So first I'd be looking for a new physician to help you. Look for a solid general family doctor that can give you guidance and do testing for Thyroid, hormones, diabetes, cholesterol and any other things that could be influencing her weight. Have the physican just talk to you so that your daughter doesn't take on any more food related issues.
Then have talks with your daughter on a regular basis. Find out without talking about weight if anything is on her mind, worries her, making her angry, is she bored, is she having trouble with kids at school or is she having problems academically and you haven't seen the struggle come through in grades yet. My neighbors child was struggling in math, got a tutor and backtracked 3 years in math and was retaught it all and the weight and stress quickly melted. Mom and daughter talks can be done while taking long walks or bike rides.
Make sure she doesn't have more inside time than outside time. Keep the junk out of the house except for special occasions, if she want to know why. Tell her special occasions don't seem so special anymore because we have this stuff all the time. Give her the park district book, or Y book and have her pick 3 activities to do. One could be a class in art or acting or science and the other 2 could be a sport, swimming, soccer, whatever to get her moving more without saying anything about actual weight loss to her.
Remove any dairy or meat grown with hormones. Don't heat or serve warm foods in plastic containers. Use glass or metal. Read up about how hormones can disrupt the bodies metabolism and help you keep on or gain weight and go into early puberty.
Good luck, it's hard to keep a chld with the mindset of a good body image, keep them happy and stress free and learn a lifetime of exercise. I wish you and her well.