I leave a detail how is this canon. (Knowing this Artist like to make fan-art represent the scene from in-game event.)
Since the Artist posted this not long after the release of Heian-kyō chepter. It's very likely this art represent the scene at Heian-kyō when Tamamo asked us(you) to keep your mouth shut about her true identity. (Tamamo named "Takako" in this chapter, Also there're no detail is she a living person or servant, but definitely not chaldea's servant.)