Karen, the 12-year-old protagonist of the novel, is a dynamic character whose journey is marked by significant personal growth. At the beginning of the novel, Karen is portrayed as a sensitive, emotional, and somewhat naive young girl who is struggling to cope with the impending divorce of her parents. Her initial attempts to deny the reality of the divorce and reunite her parents demonstrate her innocence and idealism.

As the novel progresses, however, Karen's character undergoes significant development. She begins to confront the harsh realities of her parents' fractious relationship and the inevitability of their divorce. Her experiences, including her father's slap and her brother's running away, force her to confront the complexities and challenges of her family's situation. Her decision to buy the divorce book and educate herself about the realities of divorce serves as a powerful symbol of her growing independence and self-reliance.

One of Karen's most significant characteristics is her emotional sensitivity. She is deeply affected by the conflicts and tensions within her family, and her emotions often serve as a barometer for the mood of those around her. However, as the novel progresses, Karen learns to navigate her emotions and develop a greater sense of resilience.