Who is Janey from Lonesome Dove and what is their importance?

Janey is a young girl, barely in her teens when July passes by the house she lives in, she has been bought and sold more than once already. When July leaves, Janey takes the opportunity to leave the abusive man who controls her now, and follows July on foot. So swift that she can keep up, she scares July half to death when she allows herself to be seen. She is shy with everyone but Roscoe, and convinces him to let her travel with him by telling him that she can hunt and cook, and knows her way through the country. Roscoe agrees to take her, and she ends up losing her life with Roscoe and Joe to Blue Duck.