She is wearing her diamond brooch. She only had three tiara's:
1 The Saphire parure 2 the Mellerio ruby parure 3 her diamond tiara with the stars
1 and 3 have two different ways of wearing them (the saphire tiara can be worn in the second setting seen on Mabel and Maxima) and the diamond tiara can be worn as Beatrix does or with the stars on top.
As Emma is seen wearing the diamond stomacher she got for her wedding my bet is she is wearing a diamond tiara so either the smaller setting of the saphire parure or her own diamond tiara in either setting.
--Previous Message-- : " Looks like a leafy motif.... " : : Indeed it does : Thanks so much for the photo, will be fun : finding out which jewel this might be.... : Thank Goodness the brooch is clearly visible : :