Former patient, now running the sanitorium.
I watched Nurse Christian do a dance in the sanitorium room with all the beds. It suggested that she was possessed.
Nurse Christian and the Matron have a dancing scene. I followed Nurse Christian through the forest maze until she was facing the hut. The Matron opens a window with strong backlighting and sees Nurse Christian. She comes out and they do a dance sequence, longing to be together through the woods that separate them. They run through the maze. Then the Matron runs through the iron gate at the back and locks it behind her. They look at each other wistfully and she runs off.
One on OneEdit
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Another encounter with the nurse is documented here: