During the events of Hogfather Susan Sto Helit was the governess of Twyla and Gawain Gaiter. But in the next book she appears in, Thief of Time, there was no mention of the children nor her previous position as governess. Why did she stop?
The obvious explanation is that the children became too old for a governess and Susan's position expired, requiring her to find a new job. But since this was never mentioned (and I've long given up trying to figure out how much time is between the various Discworld novels), I am sort of at a loss to what happened. Was there ever any explanation given, either in the books or by Terry Pratchett himself, or did the fans figure something out on their own?