Who is Patricia Hood from In the Lake of the Woods and what is their importance?

Patricia Hood is Kathy's sister, she is sometimes called Patty. She does not approve of John. Patricia sees news of Kathy's disappearance on the news before John contacts her. Patty says that Kathy was not happy in her role as the wife of a politician and that Kathy's affair with the dentist was nothing more than an effort to wake John to her own needs.