Who is Sally Keath from Moccasin Trail and what is their importance?

Sally is Jim's younger sister. When Jim returns to the family, she is fifteen-years-old. She is distrustful of Jim for a few reasons, one being his appearance. Sally has a strong character and sees it as her responsibility to care for the family. She disapproves of Dan'l accompanying Jim on the cattle drive and wants to protect him from becoming like Jim.