Once very beautiful and strong in the Dark Side of the Force, her appearance had degenerated to that of an old hag by the time she met Lord Scourge. Though she could have easily afforded the procedures required to restore her youthful appearance, she chose not to, possibly to flaunt her strength in the dark side or that she didn't care about superficial appearances.
Nyriss was among a group of co-conspirators on the Dark Council who planned to destroy the Sith Emperor, although she never took action. She, along with her ally Lord Scourge, was responsible for Revan's capture on the planet Nathema. She held the Jedi captive for years, until he eventually managed to turn Scourge against her. Scourge betrayed Nyriss to the Sith Emperor, who immediately launched a vicious attack on the traitors. Nyriss confronted Scourge outside Revan's prison cell and engaged him in a duel along with his new ally, Meetra Surik. Nyriss overpowered both her opponents and was prepared to strike them down with all of her power, when Revan, having just recovered his memories, stepped in and intercepted her lightning attack. The Dark Lady was burned to death when her lightning bolts were redirected at her by Revan.