"Who are you?"
And she breaks. She crumbles inside, and realizes that the day has come, and that she was right. It will kill her. In fact, if Amy, or Rory, or her Doctor were here, they would see that she is already dead. But she is River Song, and she has a job to do. So she gets up, hoping her tears will not show.
And then she has to say it, the name. And she sees the way he is floored, and realizes why he looked at her the way he did at the Byzantium. He trusts her, but it is a suspicious kind of trust. It is wobbly, but he trusts her, and she grabs that fact, and holds on to it like it is a life preserver, to keep her afloat in this sea of emotions.
But still, he is her Doctor, more so than ever, when he tries to sacrifice himself for the library. Key word: Tries. She can't have all that not happen. She just can't.
So she ends up strapped to a throne of death, listening to the computer count down the seconds till her death. But, even though he isn't her Doctor, he still infuriates her. Making her comfort him, when she's the one that is breaking inside! She really does hate him sometimes.
But it's all ok, in the end. Ok that she is the one to die. Because he has all that ahead of him. And she has nothing left.
