Replying...
Intro. Lady Maria was a citizen of Cainhurst and is directly related to Queen Annalise. However, she was one of the first Hunters to join the night hunt, studying under Gehrman, The First Hunter. At an unknown point in time, Maria lost her beloved weapon, throwing it into a well when she could no longer swallow it, and mysteriously vanished into the Hunter's Nightmare. Some believe this was related to the atrocities committed by the Hunters in the Fishing Village. It is possible that she respected Gehrman so much that she helped desecrate the village and kill Kos. Now, Maria resides in the Astral Clocktower, caring for the disfigured patients who dwell there, guarding the 'secret' of the Nightmare, the entrance to the Fishing Hamlet. She sits in a chair, seemingly lifeless...

Lady Maria of the Astral Clocktower

@James