When Did Your Kids Energy Level Change

Very normal! As kids enter puberty they go through a LOT of growing, not just physically but physiologically as well. Her body and mind are beginning the process of going from childhood to adulthood, it's a lot of work :)
I've seen the same thing with all three of my kids and I remember it myself. Especially during high school, it was SO hard getting up in the morning, and it didn't seem to matter how much sleep I got. I remember sleeping until at least noon on the weekends, and still being tired/slow when I first woke up.

have you had her iron levels checked?

other than that, this is pretty much normal!

My son did this when he hit puberty. He is now 14, and he goes strong all day long, but man, can he sleep late! I don't let him sleep the day away, and he doesn't want to anyway. He's also good about going to bed early if he knows he's getting run down.

I'm a teacher, and I used to work with a school nurse who told parents that teenagers, especially young teens, need as much sleep as toddlers because their bodies are changing and growing so much. She had documentation to back this up, but I don't have it anymore. As a parent of a teen, it sure seems to make sense.

I think it's age related...that'd be my guess.

I agree with Mamazita. This is normal. My granddaughter is 11 and acts similar to this.