Kate McNiven's Blue Stone and the Curse on Monzie

Graeme described the stone as a moonstone sapphire and said the ring in which it was set was kept in a casket and only put on by daughters-in-law who had borne an heir. She says the ring was found in a box of papers left in her mother's care while the family was abroad, so it was no longer guarded within the walls of Inchbrakie, and Wikipedia adds that the property was gradually sold away after the stone was removed from the house by mistake. She also described an iron chain charm said to be Kate's with a black heart and the words 'cruelle death'. The Taymouth Castle article gives a variant in which a Campbell of Glenorchy leads a party to drown her, and adds that she said the Campbells would have no male heir. Neither story has contemporary proof.