It was hard to resist the urge to hug Kathy, so Sarah didn't try, though her actions were careful and gentle, an embrace Kathy could back out of easily if the additional comfort wasn't something the younger girl was comfortable with.
"Sweetie, this isn't your fault," she said softly. "You didn't know, because you weren't supposed to know the difference. You were tricked, you didn't do anything bad." And if Sarah ever came face-to-face with the monster who had pretended to be Angel, she'd happily beat him.
"I'm sure Cordelia and your brother don't blame you one bit – in fact, I'd bet the thought never crossed their minds, not even once," she continued. "I know it's hard when you feel guilty, and I know me saying you're not doesn't magically make it go away, but it's still true. This isn't your fault."
The truth of the matter was, Sarah was certain that even had Kathy not been a pawn in this game, they – Darla, whoever else was invested in this – would have found another way to see this come to pass, but that was hardly the thing to comfort anyone.