Who is Sheila Kennedy from Welcome to the Monkey House and what is their importance?

Sheila is the fourth cousin of President Kennedy. The Secret Service tells Commodore Rumfoord that Sheila and Robert have been meeting secretly on boats and yachts in the harbor for some time. When Sheila comes to dinner, the entire Rumfoord family and the narrator approve of her. She symbolizes healthy, young love and promise of a normal, happy life for Robert.