I was the same way as a child and didn't learn until very much later in life that I had celiac disease and was hypothyroid. You don't mention whether your daughter's weight is isolated to the abdominal area or whether she's just overall pudgy. BUT, as a child I had a belly, but thin legs and arms. That's a sign that my intestines were inflamed due to the celiac, which is an intolerance to the protein found in wheat, rye, barley, and oats. This disease is the most underdiagnosed genetic disorder (just google "celiac" and "fasano" to find the research or check out www.celiaccenter.org). One early sign I had was that I had low iron levels, so I would recommend you get those checked as that can result in low energy in a child. Since the disease is genetic, I had both my kids tested and they both have the disease. My youngest son, who also seemed pudgy, lost that belly within 6 months (his shorts became loose and was able to wear the same ones for another two years, even though he grew in height). Another sign would be whether your daughter is short in height for her age and for your family.
I will note that as a child, my mother did just as you're doing, enrolling me in dance classes, pushing me to eat right (which I was) etc and none of it worked and I only ended up as a teen on the yo-yo diet circuit, with very, very low self esteem since it seemed that there was something "wrong" with the way I was. So, I strongly recommend you get your doctor to run the celiac panel (there's 5 separate blood tests). I imagine you will have extreme difficulty in getting the doctor to run the thyroid tests unless you have a family history of thyroid disorders, but the low thyroid goes along with the celiac in many cases.
