I am from the U.S., but I don’t agree with the U.S. protecting her. As gar as I remember, she never served any sentence, since she never returned to U.K. since shortly after the accident. The main difference between that case and this one is Diplomatic Immunity.
Sure, she claimed it, but it never truly applied to her. She nor her husband were in the diplomatic field and she fled, which gave up her immunity if she had it.