What does the bird Leigh sees after her mother's death represent?

The bird represents Leigh’s regrets at losing her mother. Throughout the novel, Leigh believes that her mother became the bird. And while this is never fully confirmed or denied, Leigh has many nightmares of her mother as the bird getting hurt or dying. By the end of the novel, however, the bird represents Leigh’s acceptance of her loss and how she is finding ways to move forward in her life.