Who is Helen Hoover Boyle from Lullaby: A Novel and what is their importance?

Helen Hoover Boyle is a real estate agent. She makes her money by selling haunted houses to people, and then reselling them when the new owners become frightened by the hauntings. Helen Boyle once had a child who died soon after she read him the culling song. She later killed her husband with the same culling song, an act that led her to embrace the power and use it to commit political assassinations in exchange for rare jewels. Over the course of the novel, Helen and Streator fall in love. Together they fight to save the world from the culling song. In the end, however, Oyster forces Helen to commit suicide.