On her fifteenth birthday she shot her father to death. She claimed he had been sexually abusing her for years, and was not convicted of murder since her story of self-defence was believed.
As an adult, when she joined IDEA, they investigated her background. They found that there had been no abuse and she had killed her father because she felt like it. She was allowed to become an agent anyway, as IDEA had uses for a natural born killer.
Later, when taking Vincent Wheaton into custody, the psychic accidentally released Ray's anger at her. It turned his body into a fireball, killing him, Christine, some tourists and finally destroying Canterbury Cathedral. (PROSE: Warlock)