What an interesting post. Thank you Arthur.
Because QEQM had so many nieces and nephews to whom she gave wedding presents, I had assumed that the tiara and brooch given to her niece, the later Princess Anne, would have been relatively modest.
I don't think that the large tiara worn by Lady Elizabeth and her daughter would fit into the category of modest.
Like Arthur I had wondered if the necklace could have been the tiara given by QEQM. (Judging by the hairstyle I think that the photo posted by Arthur is after the marriage of the Prince with the former Lady Anson.)
Below is another photo of Princess Anne wearing it.