Diplomatic Immunity for American Diplomat's Wife in U.K.?

As mentioned in class last week, there is a simmering dispute between the United States and the United Kingdom over the diplomatic immunity of an American woman who is wanted in Britain in connection with a traffic accident causing death. You can read more on the story in this New York Times report. As we take up the topic of immunity this week, which side do you think has the better argument as a matter of international law?