Luckily, she does something about it: she asks the moon, and a lady with crazy hair, and her dog, and a snake, and everyone else, "What makes you happy?" Just hearing other people sharing their idea of happiness takes her out of her bad mood, and when her ma asks her, "Did you find out what makes you happy?" she answers with a catalog of activities both shared and solitary, physical and mental, creative and silly, including, yes, taking a bath with the dog.
Prescriptive without being dogmatic, Taking a bath with the dog will be a great book to have around for the grumpy day, the day when the play date cancels or the demolition derby is rained out. Everybody has those days.