I agree with Alphaghetti, but I would also say it depends how overweight she actually is and what kind of food her parents are giving her at home. She may not outgrow it if she eats at McDonalds 4 times a week and eats doughnuts for breakfast etc. However, aside from what you are already doing (encouraging her to be active, serving healthy foods), I am not sure what else you can do...the rest is up to the parents. I agree that serving a treat once a week will probably not make any major difference...it is what she is eating at home that will make the difference.