Teenagers with Weight Perception Problems

My 13-year old is complaining that her stomach is big (believe me, it isn't at all...she has an athletic body).  She was also complaining yesterday that her legs were too long and she didn't want long legs. 

Where do kids come up with these things?  Most people love the idea of having long legs and a flat belly.  Why are legs too long and bellies not flat enough? 

If she starts trying to diet or look for natural weight loss products, I will get upset. Hopefully, this is just normal teenage complaining (she's really good at that).