Witch Wish by Jacqueline Seewald
Val Williams believes she will never be as pretty or popular as her older sister Ailene. When Ailene dumps her on an unfamiliar road after an argument, Val decides to ask directions of the only person she sees—an old woman engaged in a garage sale. Val purchases a music box that the old woman claims has magical qualities and will grant Val one wish. In a fit of pique, Val wishes that that her sister would stop being so perfect. When Ailene starts acting oddly, breaks up with her boyfriend, stops talking to her friends, starts dating a “bad” boy, and cuts classes, Val is troubled. She begins to fear she caused all this to happen by making her wish and suffers a guilty conscience. How she goes about setting matters right makes for some unusual complications and surprises.