Jest right : a Xanth novel
(Book)

There's no shortage of laughs when Jess is around; she's been cursed to have nobody take her seriously. But her dubious talent comes in handy when she meets the very handsome showman Magnus. He promises to fake taking her seriously--if Jess joins his traveling show. But first they must see the Good Magician. He will give them the use of the flying Fire Boat to tour the realm if they complete a quest. The only problem is, he can't remember what quest. Something to do with night mares, day mares, and one or two future princesses. As Jess and Magnus try to unravel the mystery, they discover their true mission: to save Xanth from a big bird with a bone to peck . . . --,Publisher's description.