Besides feeling a lot more pain the next day or the one after that due to muscle strain that becomes more painful later, there is always a possibility of concussion. If your head is violently jerked, even if there isn't a mark on it, the brain can bounce of the opposite side of the skull and a concussion can result. Something to look out for after any sort of blow or tumble. Hopefully she did not have any concussion and won't be put off cycling by this butthead driver. These kind of unforeseeable accidents can be pretty scary.