hey hun, its horrible when stuff like that happens isn't it

What sort of surface did she hit her head on?

I suggest you put a cold washer on the area for a while. Keep an eye on her for signs of concussion: vomitting, eyes rolling back, getting very sleepy... etc and also make sure the bump hasn't gone inwards, if it has, I would take her straight to the hospital.

Maybe give the hospital a call for extra reassurance.. im sure she is fine..