She comes from an abusive family of Servants, and has been hunted by both The Cold Boy and The Wooden Girl. The Wooden Girl intended her to be her next "vessel". Her physical appearance is left entirely unknown, but she was fourteen years old during her first real encounter with the Fears. She became a Runner almost immediately following.
Christie is angry and quick to resort to violence, due to her history of abuse. She leaps to defend herself at the slightest provocation, and tends to keep herself separate from others. Despite the fact that she has been running as part of a group for several years, and is well-respected as one of the most resilient and resourceful among the Runners, she still finds herself incapable of lowering her guard fully, which makes her short and terse when dealing with others.
Christie is well-respected as the leader of a small group of Runners which includes Locomotive Breath, but is not particularly friendly. She is friends with them, yes, but she is not and will likely never be a particularly sociable person.