Looking for a children’s book, brother and sister, a series of magical challenges.  One requires that they escape from a conch shell with increasingly important quotes.  They start with jokes/riddles and end up needing powerful quotes for the final sections of the shell. 

Also there is a scene where the sister (Nora maybe? Ellie?) is faced with a series of doors, each in a set of two where she chooses one based on her reflection.  At first she chooses more sophisticated versions, with fewer of her hated freckles, but ends up very uptight and opts to return and take another path.