E's explanation ...

“Come on, lie with me J, Lie here. Close. Close your eyes J, close your eyes. I love this. Silence, absolute silence.”

“Nice.”

“A pocket of absolute silence in this city, isn’t it incredible?”

“How is it possible?” I asked, “The windows are so old.”

“Mr Tournan told me that’s its all thanks to reflecting sound waves. The positioning of the buildings around the courtyard. None of the other rooms are like this at all, that’s why I have my bed in here, in the main room.”

“Why don’t you go live in the countryside instead of being holed up in Montmartre then? I hear it’s quite quiet out there.”

“The city is my life support!" she rejoined. "I need to see all those other faces everyday, healthy faces, I need to be able to recognize my place in this world, I need scale. But J, I also need the silence, after everything that happened I need solitude when I can. That’s why I can’t ask you to live here with me. I think I would go crazy if I wasn’t alone when I need to be. Now, after … 

"Those months J, those months when I flew with you, I can hardly remember anything. Just voices, voices all the time, scolding, screaming. Demons. My voice, my mother’s voice, the voices of strangers, and it took such a long time for them to leave me, even after my body was clean again. Those voices fouled my mind. And now I have this place.” She closed her eyes and inhaled deeply and smiled a smile that only someone who knew E as well as I do could recognize. It was barely noticeable, but to me it looked for all the world like she had finally been touched by sunlight once again.