Despite being a Sith her lightsaber was purple, she had no visible sith tattoos not unlike Dooku or Vader. Actress Valerie Wildman played Sariss in the video game Star Wars Dark Forces: Jedi Knight.
Sariss was a minor background character seen on the streets of Mos Eisley in Episode IV A New Hope, the Decipher trading card game described her as "The Prophetess" an Imperial informant who used her visions in the force to help hunt down Rebels. She was also said to be one of the Emperor's "Hands" much like Mara Jade and Lord Cronal.
Durinig the course of Dark Forces Jedi Knight, Kyle Katarn spared the lives of 2 dark Jedi,Sariss and her apprentice Yun, it is clear why Yun was spared, Kyle thought he could be turned to the lightside, his reason for sparing Sariss is unclear, she was not romantically tied to Kyle, he never hinted she could be turned to the lightside, the simplest way to explain her life being spared is that Kyle was unwilling to kill a woman. The more complicated reason being he viewed her as someone who could be turned to the lightside as he thought her apprentice Yun could be.