When she was younger I used to worry rather a lot about the fact that she didn't seem to sleep. She was involved in tennis, swimming, diving, football, basketball and ice skating at various points with swimming being the one she stuck with. You'd think she would be tired, but she didn't sleep. We had it arranged that the children were only allowed to come into our bedroom if there was a huge thunderstorm or they had a nightmare, so our sleep wasn't disturbed too much.
Now she's older she knows that she needs to be active after work in order to sleep or sometimes she takes Melatonin.