Who is Josie Cahill from Pictures of Hollis Woods and what is their importance?

Hollis is sent to live with Josie in the beginning of the novel. Once an art teacher, and movie-star beautiful, she intrigues Hollis because she carries a knife in her hand. Hollis and Josie run away to the Regans' summer house in Branches when the mustard woman finds a new home for Hollis, but Josie misses Beatrice and her home, so Hollis calls Beatrice to come home and live with Josie.