Who is Mrs. Windemere in Gary D. Schmidt's book Okay for Now?

Mrs. Windemere is one of the customers that Doug Swieteck delivers groceries to on Saturdays.  

In the beginning of the story, Doug and his family move to a new area. Doug struggles with making friends, and his family struggles financially. Lil Spicer is an early friend to Doug, and her father owns a local deli. Mr. Spicer kindly gives Doug a job delivering groceries on Saturdays, and Mrs. Windemere is one of the people that Doug delivers to.  

Her other important function to the story is that she (in a roundabout way) helps Doug retrieve the Large-Billed Puffins plate. Doug knows that a father of a classmate of his has the Large-Billed Puffins. Doug also knows that this father is a fan of Aaron Copland. Mrs. Windemere happens to have a manuscript edition of Copland's autobiography. She gives the autobiography to Doug. Doug trades Mr. Russel the manuscript for the Puffins.