Originally, our Empress Shangguan Linglang never took Black Impermanence Night Demon to heart. The reason she immobilized him on the spot before mercilessly beating down Third Young Master Han Ziyun, was simply because she... uh, did it inadvertently—okay, fine, it was just convenient.
Before the good-looking young soul-hooking envoy, Black Impermanence Night Demon, opened his mouth to seal his fate, the Empress only saw the distinctly different dead ghost in front of her as a regular one. She didn't have any intention to make things difficult for Night Demon really. She planned to let the little ghost go after she lectured the guy she mistook for Han Ziyue, Third Young Master Han Ziyun.