Who is Mara Jade from Dark Force Rising and what is their importance?

Mara Jade is second-in-command to Talon Karrde on the Wild Karrde. She has a weak Jedi sense, and she often suffers nightmares in which the late Emperor orders her to kill Luke Skywalker. In the course of her work, Mara is intercepted by an Imperial Star Destroyer and taken aboard. She demands to see the captain and be taken to deliver crucial information to Grand Admiral Thrawn. She identifies herself as the "Emperor's Hand" and convinces Thrawn of her authenticity.