The elderly woman who talks to Nancy about infected rats in season 3 of Stranger Things is Doris Driscoll. Nancy and Jonathan encounter her while investigating reports of unusually aggressive rats in Hawkins.
Doris lives in a modest Hawkins home and is worried because rats have been eating her fertilizer. She has captured one of the animals, giving Nancy and Jonathan their first close look at the strange outbreak. The investigation soon reveals that the rats are not suffering from an ordinary disease: they are connected to the Mind Flayer’s return and the supernatural events beneath Starcourt Mall.
Doris is played by Peggy Miley and appears in “Chapter Two: The Mall Rats.” A common mix-up is to remember her only as “Mrs. Driscoll,” the name often used in dialogue, rather than her first name. Her role is brief but important because the rat incident helps Nancy recognize that the Hawkins Post’s strange local stories are part of a much larger threat.