Catherine, eldest daughter of Duchess Danton and older biological sister to Jeanne, becomes stepdaughter to Duke Foyer and stepsister to his daughter Cinderella following her mother's marriage. Her father remains largely absent due to extended business travels, leaving her primarily under her mother's influence within the household.

She possesses brown hair, blue eyes, and fair skin, distinguished by a mole under her left eye and depicted as slightly taller than other women of comparable age. At home, she typically wears a simple blue dress and brown shoes, transitioning to elegant dresses in various shades of orange for formal occasions.

Throughout most of the series, Catherine displays entitlement, superficiality, and cruelty. She obsesses over elevating her social standing, specifically targeting marriage to Prince Charles for wealth and status rather than affection. Alongside her mother and sister, she systematically mistreats Cinderella, forcing her into servitude after the Duke's departure. This includes confiscating Cinderella's bedroom, assigning exhaustive chores, and subjecting her to consistent ridicule and verbal degradation. Catherine frequently expresses embarrassment at their association and openly mocks Cinderella's appearance and circumstances. She participates in her mother's schemes to attract Prince Charles, such as entering the Flower Queen contest and exploiting Cinderella's connection to Charles while he is disguised. Her interactions also include mocking her sister Jeanne's eating habits and physical appearance.

Her narrative role involves persistent efforts to undermine Cinderella while pursuing the prince. Key instances include attempting to outperform Cinderella in dancing lessons and reacting furiously when Cinderella excels, falsely accusing Cinderella of theft in the royal vineyard, and forcing her to complete sewing tasks during their ill-fated stint as castle maids—a scheme resulting in their punishment after discovery. She participates in destroying Cinderella's invitation to the royal ball and shredding her dress. Later, during the glass slipper test, she painfully forces her foot into the shoe only for it to pop off due to incompatibility.

Catherine's development remains minimal until the series' conclusion. Brief moments hint at potential change, such as concern during her mother's near-fatal illness or temporary cooperation under magical influence, but these shifts prove inconsistent. A lasting transformation occurs only after Cinderella's engagement to Prince Charles becomes irrevocable. She then abandons her vain pursuits, makes peace with Cinderella, and ceases her antagonistic behavior.