I would take your daughter to a nutritionist.  Just and extra 100-200 calories a day and that can lead to weight gain.  You may just be missing something.  I am a person who has had to "watch" her weight my entire life.  You may as well give your daughter the tools to make good choices about food and activity.  I know you are not alone with kids with weight problems,  it is a really tough thing as you want them to be healthy and trim but do not want them to obsess about their weight at such a young age.

I am thin now but it has taken time to get it all firgured out.  I still need to really watch what I eat, and I excercise everyday for an 45-60mins and that is just to stay the same weight.

Good luck to you and your daughter.