Who is Rachel Honaker from The Unquiet Earth: A Novel and what is their importance?

Rachel Honaker is the first-cousin of Dillon Freeman. When she is sixteen-years-old, the fourteen-year-old Dillon falls in love with her and never stops loving her. Although she resists his advances, she has deep feelings for Dillon. She has been told by her mother that when a man and woman who are related to each other have a baby, it could be born deformed. Rachel has also been told by her mother that a relationship between her and Dillon would be a sin.