Buffy's expression might have faltered while Ben continued on, but her grip on that sword never did. She was torn inside, but not enough to put down that weapon or agree to what Ben was asking of her. She wasn't stupid or naive, even if she was becoming emotional from Ben's words.
"Don't talk about her!" she shouted, voice thick with threatening tears. "Don't, Ben. Just...don't."
She sniffled a little, glanced to Dawn, then looked back at Ben. "It might not be your fault. But you're attached to the person that it is. I'm sorry..." She lifted the sword and motioned to stab it in Ben's direction.