Christine was a familiar face around the Grid. As the CIA liaison officer, she had regular meetings with Tom, which the pair of them generally spent busily trying to pull the wool over one another's eyes. Despite Britain and America's 'special relationship' MI5 and CIA seem to have little time for one another. Christine certainly gave little respect to the team. It was a case of opposites attract when a romance blossomed between Christine and Tom.
Just like any good security officer, Christine was completely loyal to her country and devoted to her job. She didn't care if she had to trample on a few British people in order to get the job done. When Tom was set up by Herman Joyce, she crumbled. Unable to take the strain any more, Christine quit her job at the CIA.