Just wanted to post an update...
Before getting in to speak with our daughter's physician about her obsession with her weight, she caught the flu bug that was going around....or so we thought. She had some vomitting and complained of stomach pains, but she had an ongoing fever that would come for a few days, then go away, then come back. We couldn't get her to eat and she was sleeping all the time.
DH took her to see the physician for her fever, fatigue and stomach pains - they did a urine analysis, strep culture, blood work for mono & a stomach x-ray. It turns out she was severly constipated (I believe due to her sudden diet changes) - so much so that it was causing the fever (usually around 102.5), fatigue and stomach pains. She is now on Mirolax for 2 months and limited to 1-2 cups of dairy per day. She has been feeling better since DH took her to the doctor - I saw her run last week for the first time in a month and I almost cried with relief.
This past weekend she started talking about exercising again, but I will say she has been better about the food aspect of her "diet." They are doing a "Keep Moving" unit at school right now, so I think that is contributing to her exercise talk.
She did lose weight throughout this ordeal, due to her weight obsession and then her illness, but is still at a healthy weight. We are going to keep working with her and the physician (who told us to call any time - they were also concerned) to make sure she stays healthy, but I have to say this has been one of the most trying things I've gone through as a parent.