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

In the 2011 children’s novel Okay For Now, by Gary D. Schmidt, Mrs. Windemere is a celebrated playwright whom fourteen-year-old Doug Swieteck delivers groceries to on Saturdays.
After moving from New York City to Marysville, New York, in 1968, Doug feels out of place and lonely in his new surroundings, and these feelings are coupled with the stress of his family's financial woes. Doug spends time at a local library learning to draw after he becomes delightfully enamored with an illustrated book, The Birds of America by artist John James Audubon. The huge book is filled with plates of the birds, which they sell off to help fund the library. As the story continues, Doug meets Lil, the daughter of a local deli owner. Lil's father, Mr. Spicer, offers Doug a job delivering groceries on Saturdays. While delivering groceries to Mrs. Windermere, Doug notices a plate from The Birds of America, the Red-Throated Divers, hanging in her house. Later on, Doug finds out that the father of one of his classmates has the plate of the Large-Billed Puffins, which he desperately wants to come into possession of. Doug learns that the classmate's father is a fan of Aaron Copland and trades a manuscript edition of Copland's autobiography from Mrs. Windemere's book collection to him for the plate.

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.