Who is Carol Monaghan and what is her relationship to the Berglunds?

Carol Monaghan is the Berglunds' next-door neighbor. She is a single mother who lives with her daughter, Connie. Despite Carol's questionable behavior (she takes advantage of Patty's offer to babysit, she ignores Jessica, and she flirts with Walter and Joey), Patty will not say a bad word about her.