From Laurel's point of view, Fay scares him to death. It is a tribute to Miss Welty's skill and fairness that we are able to entertain the notion seriously. In truth, Fay is a horror but eludes being evil. Almost one-dimensional, she is saved by being credibly stupid. Naivet doesn't make her any less destructive but saves her from being malevolent.
Laurel is too nice but escapes being a prig.
If Fay were a monster and Laurel simply nostalgic, the arena of action would shrink. What we would have would be case histories. Miss Welty redresses the balance in two ways. She does something necessary by sketching in Laurel's background in a few delicate strokes. Her childhood days at Becky's mountaintop house in West Virginia, which recall Becky's childhood as well, are the most beautiful pages in the Welty canon, extraordinary passages in an extraordinary book.