I think the one who poisoned that prostitute and the guy client it was the shinpu (sorry if misspelled) the tiny maid girl with short hair, looking at that girl's eye full of jealousy and hatred for that dancer(prostitute) since she dreamed of being on of them she poisoned her to take her place, or the other prostitutes jealous of her (the dancer) popularity with the male clients they all conspired to take action and kill/poison her( the dancer) and her client, but its just opinion though let's see on the next chapter!ヾ(☆▽☆)
I think the one who poisoned that prostitute and the guy client it was the shinpu (sorry if misspelled) the tiny maid girl with short hair, looking at that girl's eye full of jealousy and hatred for that dancer(prostitute) since she dreamed of being on of them she poisoned her to take her place, or the other prostitutes jealous of her (the dancer) popularity with the male clients they all conspired to take action and kill/poison her( the dancer) and her client, but its just opinion though let's see on the next chapter!ヾ(☆▽☆)