“My daughter is overweight.”

My 13 year-old daughter is overweight and I don't know how to handle this. 

We have always had food problems in the family as  my husband has battled with his weight all his adult life. He is a great cook and I also battle with my weight. My daughter doesn't really care about her weight and just wants to be free to enjoy her food. I find it a huge burden to try to manage her weight as well as my own and I'm becoming resentful. I've always been very careful to talk about 'health' and not 'food' or 'weight' but it is failing. She is very confident and declares that she is skinny. She knows she's not skinny so she is just being defiant in the face of pressure to conform to  her super-skinny friends. 

I just don't know how to handle it, she is at an age where she can access food so my control over the issue is diluted. Until now I watched her  like a hawk and kept her weight in check but now, finally, just as she has more freedom to eat more, she has suddenly tipped into being overweight for the first time in her life. 

It's not a lot overweight but it is there. I don't know what to do - please help!