Locked door in HS east

[Emmin]

I was exploring the east wing of howling stones with double invis and I encountered a locked door on the east side of room 14 on the map here: http://wiki.project1999.com/Howling_Stones

Is there a key for that, or can it only be opened by a rogue? Oddly enough, Drusella was up in the room (she had a mace in her hand). I thought she was supposed to spawn in room 15. Or can any random named spawn in room 15, and Drusella is supposed to spawn in room 14?