The disappearing friend mystery : the Boxcar Children Series, Book 30

The Alden children are trying to raise money for a new hospital wing and make friends with a new girl, Beth, unfortunately both attempts are proving difficult and problematic. At the same time that the Alden children's efforts to raise money for a new hospital wing are being sabotaged by nasty tricks, they find their attempts to befriend the new girl Beth frustrated by her strange behavior. The Aldens start a helper service with their friend Beth to raise money for the Greenfield Hospital. But someone tore down their signs. Who wants to stop the fundraiser?