From The Grey House:
She had been trying to come to terms with her new path since she started about seven years ago, shortly after Charlie bit her. Natalia learned a great deal about herself and the world around her, and had trained in many different areas, but through it all, she had come to one definite conclusion. She was not a Slayer; probably never would be. She tried so hard to be one, because of her history with vampires and werewolves, but the fact remained: Slayers were just as monstrous as the creatures they hunted. Humans were no less gruesome.