Whilst looking for something completely unrelated I came across this portrait. The Tenisheva's were a wealthy family so I imagine the jewels are real. The brooch itself is a beautiful piece.

https://en.wikipedia.org/wiki/Princess_Maria_Tenisheva#/media/File:Maria_Tenisheva_by_A.P.Sokolov_(1898,_GRM).jpg

I'm guessing the jewels went the way of so many of either being appropriated or being sold off to help the owner live.