Blood on Her Tongue by Johanna van Veen

In the Netherlands in 1887, Lucy tries to protect her twin sister, Sarah, who has stopped eating, speaks nonsense and has become fixated on a centuries-old corpse found preserved on her husband's estate. A doctor diagnoses temporary insanity, and Lucy fears Sarah will be committed to an asylum. As Sarah grows angry and ravenous, Lucy begins to wonder whether something has possessed her sister or whether she is simply mad. Described by reviewers as sapphic gothic horror.