Question: Why did Catherine target Nick? I know he's a big douchebag, but that can't be the only reason right? Was it to get revenge against Beth for once and all for leaving her?
Answer: Because she's insane? And very ill. And dangerous. A pure bred psychopath. She got off screwing with him, his head. She has a degree in effing with you. Beth was just a bonus. Unlucky. Collateral damage. Unfortunate. Catherine was, is a clinical psychopath. She had no reason. Or it was fun for her. She was one twisted broad. An evil dame. (IMHO).
Answer: She is portrayed as a psychopath with an uncontrollable urge to kill.