Except Riley hadn't just killed(/been heavily involved in the organisation that killed) a whole bunch of Slayers.

Actually, Buffy was pretty unsure about *Riley* when she found out what The Initiative was actually up to, going so far as to protecting Spike - who was helpless, but still unrepentantly evil - against them. And they killed *demons*, not Slayers.

Sorry, I'm blaming the glow, because otherwise... well, let's just say she'd make Bella Swan look like a sensible, self-aware feminist.