Sarah was significant as she was Abraham's wife. She was part of God's plan to create a great nation. Even though she was barren for a long time, her eventual pregnancy and the birth of Isaac were important steps in fulfilling God's covenant with Abraham.
I'm not sure exactly who Sarah is without more information from the story. But she is likely a person who has a weight problem and is the focus of the '600 pound life' story.
Some of the DCI Banks novels include 'Aftermath', 'Cold is the Grave', etc. These novels are known for their engaging crime and mystery plots. The main character, DCI Banks, is a complex and interesting detective.