Insert above the background now such a texture.



Copy this layer now and turn around the copy, applying Edit ? Transform ? Flip Vertical. Merge both these layers and change the color (Hue/Saturation)



Open now a picture representing the brooch.



Place it on a layer under the girl's one. Mark it out and erase the background which it was situated on and then decolorize the layer.



Make the brooch look bluer, applying Image ? Adjustments ? Photo Filter.



Get back to the background's layer and work with the color: make it profounder: (Curves)



Insert on a new layer the picture of a diamond.