I have a book I read in 6th grade, which was around 1992. The book itself could have been older, like 1980s. It was a definite Young Adult book even if that didn’t have the description at that time. It was about a Lady who was recently widowed, very young, who lived in a crumbling Tower (Castle). She may have had one servant. She had a Rose garden which I think was a big part of the book. A criminal possibly a thief or murderer arrives at the castle one day and stays essentially taking her hostage. I remember it was a romance. It was a really short story in a very thin book, it reminded me very strongly of “A Door in the Wall” just in terms of time. And may have been plague mentions I can’t remember. It also reminded me of Secret Garden, just because the Rose garden seemed to play a huge part in the story.