Our daughter (Age 3)has the same problem. When she sleeps, especially in the summer; even when the room is cool she will sweat. Like your daughter it seems to especially affect her hair. She wakes up whether it be from a nap or night time sleeping with sweat soaked hair. It is extremely smelly sweat also! Reminds us of raw hamburger. It is so bad that when she sneaks onto our bed during the night it will wake us up and we have to spray air freshener in the room to disguise the smell. If we bath her the night before she will need one in the morning to get rid of the smell and sweaty hair. We brought her to the DR. for this and they told us it was normal. That all children sweat. She also saw a developmental pediatrician for speech issues and we mentioned the problem to her. She didn't seem to think it was a problem either. If you find out anything different please let me know.