Maybe she did it to save a friend?We never actually see the fate of the sacrificed young woman, but we can all make our own guesses as to what might have happened, based on her expressions (which are excellent).
At first she does not seem to be worried, which leads me to a thought I have often had:-
In societies where human sacrifice was practiced, was the victim necessarily unwilling? Could it have been seen as a noble duty, to give one's life for the greater good?