Cordelia has no ready answer for that. How does one say, 'actually, Xander's going to fall in love with Buffy's sister at some point in the future' to a woman determined to have sex with the said guy? So Cordelia does the smart thing: focus on something else entirely.

She crosses her arms. "He's bad news. Way bad. I don't know why he volunteered to get you-- can you tell me what he said to you, exactly?"