The current Countess of Rosebery, her daughter, and former daughter-in-law are Patronesses of the Royal Caledonian Ball, and they are usually bejewelled for the occasion! I actually wrote two articles on the Rosebery Tiaras two years ago but haven't published them yet (I've been looking for an occasion but dates of births and marriages are really hard to find for this family), but I found some pictures of the Countess wearing what appears to be this necklace at the Caledonian Balla few years ago!