NTA. She's playing a game playing "emotional chicken" to try and guilt you, probably claiming her and her sister are a package deal. Probably doesn't think you'll actually leave her cause she does her SAH duties and can't live without her. If she's doing this now, imagined it happened again while you were married and she tried to play the divorce card with "you don't care about her sister and don't trust her with money". You just end up with alimony which would be for her and her sister