I can imagine all sorts of mischief for Rebecca at Charlotte's hands; she herself perhaps a bit bored with life and looking for something to toy with. The backstory as to how the room came to be before it was actually needed for Rebecca should be interesting, as will the actual punishment and rehabilitation portion of Rebecca's incarceration. Arty will need to be dealt with though, because he seems to be the only other living human to know where Rebecca actually is.
Thanks for sharing, I look forward to the next chapter and some explained hanging mysteries, Jackie.