Tera used to be a necromancer that worked with James Dubois within the city of Cal' Haden. Following a debacle, she was never heard from again until she appeared in the events of Ret's Rebellion.
During the A Team's mission to recover Corellon's Gaze from the High Marches' Banshees faction, Tera was present and tried to stop the adventurers from acquiring the artifact. She is shown to have been experimenting with the capabilities of the artifact on organic beings. She was chased down and eventually defeated within the tower that had served as her laboratory. Later, during the Greenwood Rebels' attempt to sign a peace treaty with the High Marches, Tera appeared again with Codrus Durane to interfere with the proceedings. when the A Team fled the scene but eventually came back in their search for Claurion Merilimbem, Tera was there again, asking them to continue the fight against the High Marches & give up on peace. Tera revealed to have been working under the Witch King and fled after failing to persuade the adventurers.
Spoilers
Tera was revealed to have been part of the Witch King's plan to have the Rebels acquire Corellon's Gaze, but make the adventurers think that they had earned the artifact.