M.F.
Wow! My daughter has never slept past 8 a.m. in her life. It's a rare day that she's asleep past 7am!
I wonder if she's waking at night without you knowing it. It could be a growth spurt. However, I might call the pediatrician about it if it lasts more than a few days. Anemia (low iron) can make people excessively sleepy.
You might make sure she's drinking plenty of fluids too.