My daughter hit her head and is complaining about a headache . she hit iit in the back of her head. about 6:00 pm or 7:00pm it is now 10:24 pm?

Head trauma: It is not uncommon to have a headache after you hit the back of your head. If she did not lose consciousness (black out), her mood is normal, is not having nausea or vomiting, able to move all extremities, easily arousable, then it is okay to watch her at home. I would wake her once or twice during the night and make sure she is doing ok and not having any of those symptoms. OK to give tylenol (acetaminophen)

Head injury: Headache following a head injury is not unusual but an examination by a physician is needed if there's associated vomiting,drowsiness,worsening headache,visual disturbance or confusion.

ER: I highly recommend to be evaluated by ER physician as this can be major issues i.e. bleeding inside skull/brain. It can be on other side concussion as well. It is better to be evaluated.