Christine is a member of the Circle of Steel, a splinter faction of the Brotherhood of Steel dedicated to taking a more active stance in the wasteland. She was a scribe in the Brotherhood before joining the Circle of Steel at the rank of Knight.
When Elijah abandoned the Brotherhood after the disastrous Operation: Sunburst, he left a trail of crimes across the wasteland. As word of these crimes reached the Circle, Christine was dispatched to track him down. In addition to avenging his crimes, she had a personal stake in the matter; he had separated Christine's lover from her. She managed to locate him at Big MT. However, once she confronted her mark at Little Yangtze, they were interrupted by security robots. The Elder escaped using the ghoulified Chinese prisoners as walking bombs while Royce was wounded and taken to the Y-17 medical facility for processing. During the course of experiments at the facility (involving jamming electrodes into the skull, and, in her own words "Making a flashlight out of [her] head"), her brain was damaged to the point of her losing the ability to read and write words properly (although she can still do equations and mathematical sums).
It was there that she was rescued by Ulysses, who blew up part of the facility just to get her out. She recovered with him for several days at Ulysses' Point, where they discussed philosophy and the failure of modern civilizations like the NCR or the Legion to forge a new future. Once Ulysses met the think tanks and received his answers, the two separated. Christine left Big Mountain with the Mark I stealth suit and resumed her quest to find Elijah. Her original armor and rifle were left behind.
She eventually tracked him to the Sierra Madre Casino, where she was captured by his slave, Dog, and forced to work for him in breaking into the Sierra Madre while fitted with an explosive collar. At some point, she was also locked in an Auto-Doc in the Villa's Medical District by Dean Domino, where her vocal cords were torn out. She later regains use of her voice when the operation is completed by the Auto-Doc in Vera Keyes' hotel room. It is there that it is revealed that her capture was part of Domino's plan to break into the Sierra Madre Casino Vault, as the elevator could only be activated by the voice of the long-dead Keyes.
If the player has at least 85 Medicine and initiates "You were badly hurt by that Autodoc" dialog line, there is an additional dialogue option when discussing Christine's love interest ("Oh, girlfriend."), and one can easily calm her down, stating that the player understands her situation; If the player has the Cherchez La Femme or Confirmed Bachelor perk there is an additional interaction with Christine when they leave her at her post before the Gala Opening. If you accept to hold Christine's hand you can promise that you will return for her.
Christine, scarred by her hunt for Elijah and unable to let him go, perished in the Sierra Madre Casino. She never completed her mission, nor did she stop to consider what had driven her to accept the mission in the first place. Obsession is another form of greed, a lesson that Christine never learned.
Christine, her mission complete, found new purpose as the Sierra Madre's warden. She watched over it silently - by choice. Over time, the ghost people came to see her as one of the Holograms. They would watch, silently, as she walked among them. At times, Christine thought of the Courier, who had kept Elijah's hand from her throat. The Courier reminded her of the other courier she had met in the Big Empty, and wondered if the two had found each other at last. She did not think of them again until she heard the legends of the Divide. The Divide, where the two messengers, the two couriers, fought beneath an ancient flag, at the edge of the world.
As a result of her imprisonment in the Auto-Doc, Christine has developed claustrophobia.
From dialogue with her it comes across that she may have gained some kind of alexia from what happened to her in the Big MT.
In Old World Blues, when speaking to Dala, you are given the option to say "The quick scribe jumps over the lazy paladin" for observational purposes, which Christine also says. The above line is also a play on the well-known phrase, "The quick brown fox jumps over the lazy dog," which itself is an English pangram - a sentence that uses every letter of the alphabet.