Bumps are so scary for moms! Your small child's skull isn't fully fused together yet and this is actually good. Not only does it enable the head to fit through the birth canal but I'm told it also provides extra shock absorption in those early, clumsy years. Bumps are normal and OK. Keep an eye on your child for the next 12 hours. If your child starts to vomit or is crying inconsolably (sign of a possible headache) or is listless and behaves abnormally then go to the ER. Those are signs of swelling in the brain/hemorrhage and can be successfully treated if you go to the hospital. Otherwise she is most likely just fine.
Last year our baby boy fell off a couch onto the hard wood floor hitting the back of his head. An hour or so later when we fed him he vomited. He vomited several times so we took him to the ER where they had to do an MRI to make sure he didn't have brain swelling or bleeding. Thank God he was fine but that was so scary. Makes you want to keep helmets on them all the time, doesn't it?! ;D