Who is Marguerite Roberts from The Man Who Listens to Horses and what is their importance?

Marguerite Roberts is Monty's mother. She plays the subservient role to Monty's, and though she occasionally tries to stand up to him when he is abusing Monty, she almost always complies with her husband's wishes. Marguerite dedicates her life to her husband and father. Very few people show up to her funeral.