>actually only two can kill her. Either Tyrion or Jamie.<
Even if Tyrion turns out to be the third head of the Targaryen dragon, he would still be her half brother. Jaime, of course, is her twin.
My choice is Tyrion, if nothing else because Cersei has been trying to kill him for years.
I believe it will be Jamie. Cersi has a bad habit of jumping to the wrong conclusion and making enemies out of friends.