Bell the Harlot
The never seen ghost sweetheart from the House on the Hill.
Bell was never seen, but places she recently left had a perfume smell.
From what Baelamus said, Bell was a beautiful harlot that worked in the House on the Hill while it was still in business. She was nice, but embarassed about her earthly remains. Baelamus kept her safe, and said she was great company for who knows how long they were there.
After the “Monk” was killed and the bodies buried, Bell was nowhere to be found. Baelamus later remembered Bell never felt right about having never been buried and having her killer, the “Monk”, in the same building. It was assumed that she was now at peace.