The "Gothic governess plot but with hypercompetent survivalist writer as the protagonist" does sound super interesting, and I'd totally read a series of books that are just Gothic governess plots but with protagonists from wildly different genres.

a fair and interesting conclusion to make, except that the book weights the scales because we never see anybody who is grieving the dead girl! We're told she has concerned parents, but they're never onscreen; nobody we do see onscreen remembers her fondly...they're not people the way that the people our protagonist has gotten to care about who loved this murderer are people, so of course he comes down on their side That is stacking the deck. This kind of reminds me of the second Hilary Tamar book, where the murder victim is also a young, unexceptional woman who's pretty much only tolerated by everyone, and no one is grieving that heavily over her death, but Julia still pushes for an investigation into her death at a time when everyone thought it was suicide/an accident. And by the end it's clear she was a pretty unpleasant person, but still distinctly a person.