Who is Isaac Lingerle from Dicey's Song and what is their importance?

Isaac Lingerle is a music teacher. He works at Maybeth's school and believes she is musically gifted. Lingerle arranges for Maybeth to have extra lessons twice a week after school. Over time, he becomes a friend to the Tillermans, often attending family dinners and helping out by babysitting for Gram. In the novel's conclussion, it Mr. Lingerle gives Gram money that allows them to bring Dicey's mother home after her death.