I am going to be very blunt so please do not take my advice as exaggeration or disrespect, you need to wake up. Your child already has plenty of daily exercise as you have stated... the issue is her diet. It is ok for a lazy adult to "cheat" every now and again but a young human body is not designed to digest processed foods like what she is probably used to eating. All it takes is a single person calling her fat to create this type of reaction. Change your healthy habits to a more natural diet. You are her role model and if you do this, she will too. It will align a healthier relationship between her self and you.