There was also that judgement in her mother's eyes and voice when Buffy "killed" the "man" that might have become her stepfather. And yes, he did hit her, but not spank her.
Ah, thanks to fans I've found that episode.
http://buffy.wikia.com/wiki/Ted - and I think that Ted might have spanked Buffy once he had her down in that bunker if she was a normal girl. Since she wasn't, she exposed the fact that Ted was a robot.
Back to shows where mother might spank their daughters - Judge Judy, the People's Court, and all of those other court shows, Often a girl (or more than one girl) is revealed to have lied about what happened, and the truth sinks her family's case. Whether it's who was driving, who the girl handed her keys to, who lent money to who - countless lies have been exposed on that show, most of them from teens (or early 20s!) who should know better. Sometimes the parents choose to continue to believe the disproven lie, other times you can see them getting mad when the judge proves that it was their daughter who was drunk behind the wheel or lent the car to a friend who didn't have insurance (or even a driver's license).