This unnamed woman is a resident of Grand Rapids, Michigan.
This woman lives next to a house which came to house a Soul Eater. When one of the house's occupants, Will Henderson, falls into a coma, hunters Bobby Singer and Rufus Turner pay the house a visit. Suspicious, this neighbor calls out to them to know what they want.
Bobby flashes his FBI badge and tells her it's just an investigation and it's their business. This woman argues by saying she is in charge of the neighborhood watch, and demands to know what their business is. In retaliation, Rufus rudely tells her off, much to her disgust.
Years later, this woman encounters two more FBI agents, who are in fact Sam and Dean. Since she is still the head of the neighborhood watch, she asks to know why FBI keep re-visiting that house. She tells the brothers about how rude the previous men were. This informs Sam and Dean that it was Bobby and Rufus who visited last time.
Once the case is solved, Sam and Dean wave to the woman on their way out, coincidentally exactly the same thing Bobby and Rufus did when they left.