As Darth Revan and Darth Malak rose to power with their new Sith Empire, Yuthara left the Jedi and joined their cause. There she was an apprentice of the Sith Master Uthar Wynn, the Headmaster of the Sith Academy on Korriban during the Jedi Civil War.
Yuthara has been planning for years to overthrow Uthar and assume control of the Academy. This planned pushed forward when the amnesiac Revan came in search for the Star Maps, ancient artifacts that pinpoint the exact location of the Star Forge. Revan has been assigned as Yuthara's apprentice, and she has trained Revan in the Sith ways e.g. The Sith Code.
When Revan and Yuthara confronted Uthar in the Tomb of Naga Sadow and defeated him, Yuthara turned on Revan but was no match for his power. Instead of killing her and claiming the title of Headmaster, Revan spares her life and convinced her to turn back to the light and join the Jedi Order again.