Sherry is a spy like the one Sayid engages in Berlin. She is placed in the social environment of Juliette's Ex-husband to make him spy on Juliette's work. When Richard Alpert notices that the other side is close to catch Juliette away from them he has to improvise: He makes Ryan drive a bus that kills Edmund Burke and simoultaneously makes Juliette feel guilty because of a similar utterance of her. This way they succeed in making Juliette agree to get to the island. Ironicly Ryan is later killed in the same way by Hurley.