Not much of a spanking. The rectal thermometer was a nice touch. But if you want them to feel it, use a horse thermometer. Just be careful not to perforate the bowls. If used correctly it will humiliate them and make them rethink their future options.
Good to see Mom knows how to get an _accurate_ reading of the girl's temperature; I agree with the other people saying the thermometer needed to be up her ass for a few minutes though