As far as I know, the pearl and diamond brooch with the portraits of Tzar Alexander III and Tzarin Maria Feodorovna (née Princess Dagmar of Denmark) does not belong to Princess Elisabeth, but is part of the Crown Jewels kept at Rosenborg Castle. It can be seen here at the bottom right of the picture, next to the brooch of the emerald parure:
But Princess Elisabeth owns and occasionally wears another brooch in diamonds, probably by Bolin or Fabergé, depicting a Russian imperial crown: