Who is Una Spenser from Ahab's Wife, or, the Star-gazer: A Novel and what is their importance?

Una Spenser was born in Kentucky. She had loving parents until she was twelve years of age and her father became violent. They clashed over religion. The violence became so bad that her mother sent her to live with her aunt and uncle at their New Bedford lighthouse. When she is sixteen, both her aunt and mother become pregnant. Her father kills himself. Una dresses as a man and secures a job as cabin boy on the whaling ship Sussex. She uses her father's name of Ulysses Spenser. Giles and Kit, two men she met on the island, work on the ship. The Sussex is sunk by a whale and Una, Kit, Giles and ten others are adrift in the whale boat. When they run out of food and water, the resort to cannibalism. Una, Giles and Kit are the only three survivors. After Giles' death, she marries Kit, who goes mad. She brings him back to Nantucket on Captain Ahab's boat.