That's very young to be having headaches. Most often adults get headaches related to stress. Most children just live in the moment (wish I could recapture that simplicity again). Does she have allergies that might be causing sinus headaches? Those are quite painful. She could have a sinus infection too. Her pediatrician might be able to help. See if you can get your daughter to explain what she's feeling so you can pass that information on to the doctor. She'll probably be more willing to talk to you than a stranger in a white coat.
how are we supposed to know the cause of them. take her to the doctors!!!
it could be she needs classes
caffeine
stress
anything