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.)