Who is Carolyn Harmon from Gap Creek: A Novel and what is their importance?

Carolyn Harmon is Julie's youngest sister. After Masenier dies, Carolyn is spoiled as the youngest child, and as a result, she is more prim and fanciful than the rest of the girls. She visits Gap Creek when she is fourteen-years-old, and she spends the entire vacation flirting with Hank. It's unclear whether or not Hank has an affair with his young sister-in-law, but Carolyn leaves soon after accidentally lighting her dress on fire in the woods.