The Golly Sisters Go West by Betsy Byars, Harper & Row, Publishers, 1985, Picture Book
May-May and Rose are the singing and dancing sisters. They decide to take their show west, but keep telling their horse to “Go,” but he won’t pull their wagon. Then Rose remembered the horse word for ‘go’ and said “Giddy-up” and the horse went. But how were they to stop him? Rose said, “Try ‘Whoa!’ It worked. They were on their way west.