Where the heroine robs the hero of magical treasures and then gets turned into a donkey by him, along with the witch who directed her, and nevertheless ends up marrying him.
Which is a suitable allusion for the heroine's story, and will make her sad and angry, but -- I know one where she's not a princess, and one where the hero sanely does not marry the princess but goes back and marries another woman who didn't steal from him.
Hmm. . . there are other variants. . . or maybe I should just tell a tale where the princess cuts off the heads of suitors who fail to answer her riddles, and the one who does answer still marries her when he succeeds. It's shorter, which may slither into the longer story more easily.