In the book Wives and Daughters by Gaskell, Molly and Cynthia are step-sisters. At first she enjoys having her sister around, but then she begins comparing herself to her younger step sister. Her new sister is prettier and is more than interested in the same boy that she is. Later on in the book, when Cynthia gets into trouble with Mr. Preston, it is clear that Molly does view Cynthia as her sister and comes to her rescue.