Buffy didn't want the girl humanized. It undermined her plan to twist her into the villain: an example of what Buffy'd nearly become and could never allow herself to be. She'd done the same with Elizabeth when Elizabeth had moved in. Coming to terms with what the Pirate King had done to Jack would have required her to forgive herself for killing Angel. Buffy led others by example and led herself by others' examples. Cautionary tales created and enforced only in her own mind.

"She'll know," she said. Hollowly. Almost dispassionately. "How could she not?...After all you did."

Now who was the merciful one? Not her. Not her at all.