Who is Margaret from the novel, Imagine Me Gone?

Margaret is John's wife and the mother of Michael, Celia, and Alec. She has a sister named Penny. She meets John in England, finds out that he suffers from depression, but decides to marry him anyway. They are already engaged when she finds out and her decision could be related to this fact and her happiness that she was the not "doll in the house" (19) of her mother's imagination.