You're a slightly overweight, but not serious. I think some people here don't appreciate that most children around puberty can differ wildly; but as you've already got a daughter that changed and grew slim, then it's more than likely that the second one will as well. In todays social media society, any girl that isn't obviously heading to be a model, is bound to be insecure, but I'd like to know why the schools sending out letters at her age. Sounds like more knee jerk reaction to the govenments obesity strategy.
And whilst I'll agree with the general rule of calories in and excersie reversing that, everyones different. Ain't nature grand, and diverse.