This is a very interesting thought, which makes my head hurt a little. I will think about it later. Meanwhile, just leaving it here…
Edith is just crazy, she began to go mad after the passing of her mother, then increasingly so after her father’s unfortunate (truly accidental) slip-and-fall death…Allerdale Hall is actually an asylum husband and wife, Thomas and Lucille Sharpe, run . Lucille is quite strict, more focused on running the place as one would a corrections facility and finds Edith’s behavior both irritating and disturbing; she’s in favor of lobotomizing the girl, but for now simply (slightly) over-medicates the girl with sedatives. Thomas is more focused on the potential for recovery and curing the patients; he promotes Edith’s flights of fancy and encourages her to write as therapy.
…Sounds like a potentially fascinating AU…
(Perhaps Alan is a childhood friend of Edith who aides in financing her stay/care there and occasionally visits??)