Who is Lucille Stone, Ruth's younger sister from Housekeeping and what is their importance?

Lucille Stone, Ruth's younger sister, is described as red-haired and outgoing. While they were young, Ruth and Lucille were inseparable allies. Lucille is, from an early age, more assertive than her older sister, but until Sylvie takes over care of them, the two have been united in the effort to survive. Lucille approaches adolescence at the same time that Sylvie turns their daily life into a downward spiral of disorganization. Lucille asserts herself and begins to grow up when she looks outside the chaos of her immediate family situation and longs to escape to a more normal life. Tentatively, but with great persistence, Lucille ingratiates herself with girls at school and with her teachers. She tries to bring Ruth along as she gradually expands out of Sylvie's realm, but Ruth cannot fit in and does not want to try. Lucille is grimly determined to escape, but in order to go to a new, more orderly life, Lucille has to leave Ruth behind.