Who is Swan, or Sue Wanda, Prescott from Swan Song and what is their importance?

Swan is the central character in the story and also the novel's namesake. As a child she is timid and serious and has been lugged around to boyfriend after boyfriend by her mother, who calls them her "uncles." Swan has an affinity for growing things and feels life in the soil of the earth. She and her mother Darleen are trapped underground with Josh and PawPaw after the explosion, though Darleen and PawPaw both die in the basement. Through PawPaw, Josh is warned to protect the child, and during their time in the basement he notices mysterious green shoots where Swan usually sleeps.