This is a good one... she always seemed like a lot more then just a werewolf. Had they not just wanted to write Oz out, she could have been an antagonist for a few more episodes. A flip of Oz's cool good guy, she could have been a manipulative psycho whose predatory nature made her want to kill. Maybe Buffy had killed one of her earlier mates in a her early slaying days... or perhaps she has a some sort of ongoing vendetta against Willow for taming Oz. To often werewolves are depicted as only sad cursed humans who aren't at fault for their actions as the wolf... but flipping the script, and having one own their nature and relish the violence they inflict would be a great ongoing enemy.