Elsa: Anna! You hold a grim destiny in your hands, sister. But it is not your own.
Anna: Elsa! By all that is holy.
Elsa: The snow's curse sealed my fate. The world of the living can no longer comfort me. Place the crown upon my head, Anna. Forevermore, I will be the jailer of the ice.
Anna: No, old friend. I cannot…
Elsa: Do it, Anna! You and these brave heroes have your own destinies to fulfill. This last act of service… is mine.
Crown is placed upon Elsa's head
Anna: You will not be forgotten, sister.
Elsa: I MUST be forgotten, Anna! If the world is to live free from the tyranny of fear, they must never know what was done here today.
Crown is fully donned, and the lights on Elsa's eyes turn blue.
Elsa: Tell them only that the Lich King is dead, and Elsa died with him.
Elsa freezes over.
Elsa: NOW, GO. LEAVE THIS PLACE. AND NEVER RETURN.

That is one cold stare she is giving…