Who is Ruth Thomas-Wishnell from Stern Men and what is their importance?

The novel's protagonist, known by her maiden surname, Thomas, until the Epilogue when she marries, Ruth is described as having a difficult birth in the last week of May 1958, during terrible storms. She is the daughter of Stan and Mary Thomas. Her father is a native Fort Niles Island lobsterman and her mother is a former servant from Concord, NH. The pretty baby grows into a very pretty girl, with remarkable posture and striking presence. Her first word is a firm "no." At age four, Ruth is abandoned by her mother under mysterious circumstances and attaches herself to the neighbors, the Pommeroys and becomes the lone girl in a pack of boys. As she loves fun-loving Rhonda more than her mother, this is not traumatic.