Cora's motivations primarily revolve around her relationship with her brother, Ruky, and her desire to care for and protect him. This aligns with the response:
Her desire to get her brother back sets the main plot in motion.
Cora's protective instincts and her efforts to look after Ruky drive the story forward and influence the unfolding events. Her actions are deeply tied to her role as both a sister and a caregiver, which in turn shapes the narrative and its resolution.