Overachiever doesn't even begin to describe her.
-- Amy (Narration) (chapter 3)

Importance: Although Amy and Sylvie are both generally competent and self-possessed, one of the main differences between them is that Sylvie is an overachiever, while Amy has more modest personal goals and also has been hindered in her goals by personal challenges. Nonetheless, Amy is not jealous or spiteful towards Sylvie. She hopes that Sylvie is safe and that Sylvie's competence has kept her secure.

Helena made sure I knew she was not my mother.
-- Sylvie (Narration) (chapter 8)

Importance: One of the most dramatic character dynamics in the novel is Helena's consistent spite towards Sylvie. Helena disliked Sylvie when she was a child, and she still dislikes Sylvie as an adult. Sylvie does not know why Helena hates her. The narrative eventually reveals that Sylvie is the illegitimate child of Willem and Ma, and thus Sylvie is a painful reminder to Helena about Willem's infidelity.

Sylvie rescued me...
-- Amy (chapter 14)