Who is Evie from Earth Abides and what is their importance?

Ezra brought Evie along when he arrived back on San Lupo Drive. She was apparently about five or six-years-old when the virus attacked and had survived by eating whatever she could find, mostly from cans. Evie grows into a beautiful young woman and is not many years older than two of the boys of the tribe, including Ish's own son. However, the older ones teach the younger men that Evie is not to be touched, fearing that she'll have half-witted children who would become a severe drain on the small self-contained society. When Charlie takes her sexually, the others are forced for a time to restrain her physically inside the house. She seems to want to find Charlie. Her condition is not mentioned again until her death some years later.