Who is Mara Jade from The Last Command and what is their importance?

Mysterious Mara Jada has a long history prior to the opening of this novel, all of which is germane to her behavior but which comes out bit by bit in the course of the novel. Stolen by the Emperor from her parents as a child, Mara is unorthodoxly trained in use of the Force, and serves as the "Emperor's Hand," carrying orders throughout the Empire. She lives comfortably in the Imperial Palace and hears the Emperor's voice everywhere.