My granddaughter is 6 years old and in the past year has gained a lot of weight, she currently weighs 90 lbs. Her tummy is very hard. She is very active...rides bikes, plays outside, runs, swings, climbs hills, hoola hoops. Her mom has changed her diet over the past year and put her on nonfat milk and lots of greens. She still seems to put on weight. Any ideas?