No matter what, my three year old will wake up anywhere from 6 to 6:45.

Last night she got 9 hours of sleep, which means I let her nap for 1-1.5 hours. I'm finding that lately she only gets 10ish hours of sleep. If she doesn't nap, she starts to crash at 4pm and turns into a scary monster.

Even when she doesn't take a nap, she will only sleep 10 hours at night. One time she went to bed at 10:30 and woke up at 7:15! Once in a while if she wakes up at 6, I can get her to fall asleep by 7, and she will sleep for another 1-1.5 hours.

Is it normal to have this little sleep? Is she not stimulated enough? There shouldn't be any environmental reasons waking her up - we have blackout shades, white noise, etc.