اSarah is Lynn's beautiful elder half sister. She is the firstborn daughter of Viscount Marble–George Russell and Lady Frances Russell. She is 5 years older than Lynn. Cold and distant at their first meeting, Sarah is actually kind and caring. Gradually, she cherishes Lynn as if she is her own younger sister, spurred on by their same state of being motherless, and defends her from the abuses of the Waveburys.
Unlike Lynn, Sarah doesn't have any memory of her mother since she died before she could even remember. Her mother's only keepsake is the flute and the musical score. She is very good at painting and an excellent flutist. Sarah has feelings for Arthur and is conscious of Lynn every time she saw them having fun together.