Mrs. Drover The Demon Lover

"The Demon Lover” is a confusing short story because it can be interpreted in different ways. Some people might consider it a ghost story. Others might think it is a psychological thriller, which makes sense due to the fact that Mrs. Drover presents signals of having a mental problem. However, I decided to go with the ghost story for two reasons: it makes it more fun and I feel like there's more evidence I could use to support that statement, even though I do agree she has some kind of mental problem. Here are the points I think support my point.

The letter Mrs. Drover received is the main point why this could be a ghost problem. At the beginning she seemed really tranquil and she didn't seem to have any problem. She seemed to be really surprised when she saw the letter in the table. I don't think she wrote the letter and placed it there because they have been in war and she has been living in the country for long. She did make a point when she says, "Who, in London, knew she meant to call at the house today?” And about the letter, even though she seems mentally ill, she did seem surprised and she made another point, "Letters dropped in at doors of deserted houses do not fly or walk to tables in halls.” Who could have left the letter there, if there are no signs of a broken window or door?
She could have imagined it due to the fact that she was already scared of the letter. But due to the fact that I believe it's a ghost story, it is weird she felt that because the letter was addressed to her with that exact date she went back. Besides that, it is really weird that it talks about the marriage promise and that it mentions, "You may expect me, therefore, at the hour arranged. Until then . . . K.” What is that hour