Lady Cory is indeed wearing the large diamond spray in Kasper's photo. It's just so much larger than one would assume on first sight and is literally covering the whole width of her bodice. The three very distinctive, delicate parts on the right of the brooch are clearly visible, the middle one touching Lady Cory's upper arm. (One can see the small feathery leaves and the trefoil diamond berries). Also the large blossom is visible (and it isn't even the largest in this enormous brooch!), as are the two small leaves right above the blossom.
The V&A website
lists its dimensions: 27,5 x 15 x 4 cm