Molly was an orphan girl found by Gundren Rockseeker and eventually dropped off with Bart who runs an inn in Phandalin. Since then she has been so helpful to the operation of the in that Bart refers to her as the Assistant Manager.
One day, Molly ran away with the Cult of Secrets who promised to share secrets with her. That didn't last long. They were creepy and liars to boot.