What is the importance of Elena's doll in the novel, The Lost Daughter?

Elena's doll, Nani, is perhaps the central symbol in the novel, representing different facets of the mother-child relationship to different characters: while Nani represents love and loss to Elena and her family, to Leda, her secret possession of Nani represents an ability to control the mother-child relationship, something she feels she does not have with her own children.