A female Jedi was a member of the Jedi Order during the Jedi Civil War. At some point near the end of the war, she was captured by the Sith trooper Atton Rand. She was able to show him his potential, and warned him that if his fellow Sith found out about him, they would break him into their ranks. Shortly after she was killed by Rand, for showing him the Force.
A female Jedi was captured by Atton Rand near the closing days of the Jedi Civil War. She confronted Rand and informed him of his Force-sensitive nature, warning him that the Sith would undoubtedly come after him and break him into a Dark Jedi if they found out. Rand believed her since he had already heard rumors of disappearances of those who were found to be Force-sensitive in the ranks, but his hatred of the Jedi wouldn't allow him to see reason, and in retaliation he nearly tortured her to death.
Then just when he thought she would die, she awakened the Force inside him, and allowed him to see life, to see what he was doing to it all around him by harming others. In response, he killed her. Disillusioned and pained with self-loathing, he deserted the Sith and went into hiding until the end of the war.
During Rand's journey with the Jedi Exile Meetra Surik he later revealed to her his past and that at first, he thought he would love to kill her, but at the end he killed her because he loved her. Rand's carefully woven web of lies eventually came crashing down; while on Nar Shaddaa Surik was approached by two Twi'leks refugees who told her that they had seen Rand when he was first in hiding there, and that he wasn't a mere smuggler, but a murderer. She confronted Rand about this, and while angry at her persistent questions, she had earned enough of his trust at this point that he told her the whole truth about his past. She forgave him for what he had done and welcomed him to stay with her on her journey to stop the Sith, and at his request she awakened him to the Force once again, and trained him to become a Jedi Sentinel. In this he became more and more loyal to her, starting to care deeply for her safety and welfare.
This Jedi was first mentioned in Star Wars: Knights of the Old Republic II: The Sith Lords during a conversation with Atton Rand.