Vergere spent time as both a Jedi and a Sith in several books in The New Jedi Order book series. Vergere has so far only appeared in Legends books. She debuted in the novel Rogue Planet by Greg Gear and also appeared in the James Luceno novel Cloak of Deception.
During her time with the Dark Side Vergere spent several decades living with the Yuuzhan Vong. Her tears could be used as both an antidote to poison or a poison itself. Learn more about Vergere on her Wookieepedia page.
Check out the entire list of women in 365 Days of Star Wars Women in the Women in Star Wars Index. It includes highlights from each post plus notes which posts include new 365 interviews with actresses, writers, artists, and more.