Who is Helene from Play It as It Lays and what is their importance?

Helene is married to BZ, one of Maria's closest friends. Over the course of the novel, we see Helene as a positive influence in Maria's life...... at least until we learn that she is having an affair with Maria's husband. After learning of the affair, BZ takes his own life..... something for which Maria places all the blame on Helene. In the end, it is Helene who is responsible for Maria being institutionalized.