Book six in the Frog Princess series.

Emma and Eadric have a daughter with a bad temper. Not too surprising, except that Millie turns into a dragon every time she loses her temper. After a disastrous birthday party, Millie sets off on a quest to find a witch who may be able to help her. Unfortunately, the road to the Blue Witch is not an easy one, and Millie and her companions may end up lost in the icy north forever.

Funny.