Lots of people near me do pole dancing as an exercise, if the video was of her dancing as an art form rather than for money in a seedy club/round a lampost while drunk/in the bedroom for a partner I don't see why its an issue (not that her doing it for a partner is an issue but posting it to facebook would be).
Teachers do need to be careful about posting on facebook though, some parents are judgy and students might see it (depending on the age you work with) and most schools expect staff to be a good role model at all times. In theory a private facebook account should be ok but as she's found out private still means anyone on your friends list can leak things so its best just not to post anything you wouldn't be happy to share with the school.