there are only a few things that warrant a spanking IMO - this is one of them (not that u can do that, but like u said...if she were yours)!
i used to argue with my profs. about it and say "a spanking hurts a lot less than being ran over by a car."
i would do what laundrymom suggested with the backpack until you can do what nan suggested. i'd probably stick a brick in there too just bc i'm nice.