Okay, let me take a look.
2 Intrigue to spot the trapdoor:
View attachment 3112508
3 Defiance will give the option to Lunge at her:
View attachment 3112521
Lunging at her wrests the bottle from her hands, and you can choose several outcomes, among them locking her up with the Pigboss (scene), feeding her what she tried to feed you (killing her) or Releasing her, which kicks you out of her house.
I tried several different stat combinations and they ahd the same outcomes, so i loaded up my own save and looked through the Gallery, and it seems that CG is used somewhere else. It seems to be the encounter CG if you try and find Marie's ring and hide from the Pigboss in the wrong place. You can still see the cell background from Gilly's basement in it too, so i guess i misremembered based on the background.
In the gallery, it can be found in the bosses section, unlocked with 2 Monster Tokens.