Lucy mentions her Aunt Marion on various occasions. On the first occasion, Lucy has failed to talk Schroeder into the idea of marriage, irritating him to the pint where he leaves the room. Annoyed, Lucy turns and mutters "My Aunt Marion was right. Never discuss marriage with a musician". On the second occasion, Lucy tells Schroeder that her Aunt Marion told her not to fall in love with a trumpet player. When Schroeder points out that he doesn't play the trumpet, Lucy smiles at him and asks how she knew she meant him. She then turns and smiles, thinking she has successfully confused Schroeder.
On Beethoven's birthday of 1980, Lucy tells Schroeder that her Aunt Marion was born in bed, "to be close to her mother".
On the 13th of June, 1991, Charlie Brown sees Rerun walking along with a blanket in his mouth. When he asks Lucy if it is Rerun, Lucy replies that Aunt Marion says "you can choose your friends, but you can't choose your relatives".