My niece had surgery to repair the jaw bone from popping out of socket. she started having small seizures a few days later. can stress cause this?

Yes: Seizures can be brought on by electrical activity in the brain but also by stress. When seizures are brought on by stress, they are called psychogenic non epileptic seizures. Be sure to get a diagnosis because new onset seizures should always be worked up, especially in someone with recent surgery. Infections from jaw surgery can spread to the brain.