Who is Littless from The Nick Adams Stories and what is their importance?

Littless is Nick's younger sister who features prominently in "The Last Good Country." When Nick chooses to run away from home to avoid being taken to boarding school for violating gaming laws, Littless comes along with him and helps him live in the wilderness. She obviously looks up very much to her brother and is eager to try to help him out and please him whenever she has the opportunity. They are very close with one another and Hemingway mentions in the opening of the book that the two have a relationship that is exclusive of other members of the family.