Fascinating discussion! Looking at the structure, I'm convinced that the Countess is wearing bracelets as bodice ornaments with her Tiaras, especially at the Coronation! Looking at the size of the stones, I have a feeling they may be Indian, and the Tiara itself looks quite Edwardian. Though I have no proof, I think this piece was sold sometime between WWII and the 1960s!
Regarding the Sapphire Tiara worn by the Countess at her Presentation, I believe it is the Tiara worn by the current Countess and her mother-in-law at their Weddings!