My observation is, that 'The Rat Queen' can spawn in place of any 'a diseased rat' in that area:
- 'a diseased rat' in the room with the junk pile (marked on the map)
- 'a diseased rat' in the room with little pond (the room with a door, east of the one marked on the map)
- 'a diseased rat' roaming up and down the northern ramp leading to
Olgor the Finder (Purveyor of Misplaced Items).