Breanna Ashworth in the Oraculum
The Oraculum is an arcane device located inside the Royal Conservatory, on the second floor. It maintains the connection between Delilah and Breanna Ashworth. It also keeps all the witches inside the Conservatory awake.
To eliminate the Curator non-lethally, you must find some Discarded Lenses and install them on the Oraculum, then pull the lever. This de-activates the machine and severs Breanna's tie to Delilah. It also knocks out all the witches inside the Conservatory.
Beside the lever, on a small table next to a pillar is a health potion above which is posted a Warning from Breanna Ashworth.