I agree with kuraiza and n2l. I'm also a bit worried about the long term effects all this focus on her weight will have on her.

Puberty is a CRUEL CRUEL thing. Perhaps you could see your GP by yourself and express your concerns. Is she having regular periods yet if at all? Could this be a contributing factor? I gain around 2kg when my period is due. Which is very annoying, but hey it's part of being a woman.

I would be stressing the importance of healthy eating and being active (which you are) rather than noting she's gaining 200-300g a week, I'm sure you are doing everything in your capable hands to keep her healthy. She will probably put weight on through puberty like most of us do.

Hope my post isn't too mean as I sincerely don't intend it to come across that way.

Eta: onyx is on the mark too!