Who is Anne Robicheaux from Black Cherry Blues and what is their importance?

Anne Robicheaux is David's deceased wife. She is murdered during a break in at their home. Over the course of the novel, Anne visits her husband in dreams.... sometimes even in daydreams. Her appearances work to aid her husband in dealing with his grief, encourage his sobriety, and even help him locate the bodies in the case he is working on. When the case is solved and concluded, Anne visits end.