The history of our civilization is filled with acts where one sacrifices for another - often for people unknown to them except for a split second earlier. In a sermon I heard at a funeral a while back when someone I knew died saving another, the minister noted that sometimes God simply calls for an angel and someone steps forward because God picked them to that mission.
Christine's parents had her organs donated and one/some found a home in a young person in Boston. No one can confirm this for sure but it looks that way at this point.... and that is the way God seems to work in these areas. Christine didn't step up to die. She was called to it. One has to have that faith otherwise there is no explanation that can possibly make sense or can calm the grief.