Cathy, the granddaughter of the infamous pirate Captain Flint, carries a lineage that defines her and binds her to the treasure central to the film's plot. Initially found as a prisoner, she is feisty, resolute, and resourceful. Her intelligence, aloof demeanor, and crafty nature make her a compelling figure, marked by strong self-reliance and a tough, surprisingly badass aptitude for outwitting antagonists.

Her primary drive is to reclaim her grandfather's treasure, a goal that fuels her distrust of others—exemplified when she immediately steals the recovered map from Jim. She forms a hostile partnership with him that swiftly evolves into loyal friendship. A pivotal moment arises when she sacrifices the final secret to the treasure to save Jim from Captain Silver. Though occasionally in vulnerable positions, she consistently proves her capability, subverting the damsel in distress trope by outmaneuvering villains. After a storm wrecks the ship, she is captured by pirates and forced to lead Silver to the treasure in exchange for her friends' safety.