Perhaps you're referring to "The Ghost King's Medicine Poison Concubine" or "The Ghost King's Seven Nights Extinction of the Favorite Concubine". These two are ancient romance novels. One of them is about a killer with unparalleled medical skills who transmigrated into a concubine, and the other is about the notorious Demon Palace's eldest daughter, Poison Concubine, who was broken off from her engagement and then was broken off? Poisoned to death? Assassinated? Killed in various ways? The details might be different. I hope you like this fairy's recommendation. Muah ~π