Who is Fay Taft from Taft and what is their importance?

Fay Taft is a young woman from Coalfield in east Tennessee who moves to Memphis with her mother and brother after her father dies suddenly. At the beginning of the novel, Fay gets a job at Muddy's waiting tables. Every evening she works, her perpetually high brother Carl comes with her as her ride. One night, Carl disappears and John Nickel helps her search for him. After they pick him up off the street and take him home, Fay asks John to take her to his apartment. He refuses, but the next day they drive to Shiloh on a whim. At the battlefield park, Fay looks at the tombstones, and John holds her.