First, I've found another version of that photo:

Between The Duke of York and The Duchess of York is Princess Helena Victoria of Schleswig Holstein.

Side by side, I think we can say that the tiara may be the turquoise one on the first photo posted by Beth. The general shape matches.

For the necklace, I think we can say that its not the turquoise one...



Here, I circled in red an element I think are the same on both tiaras.



What do you think ?

J-F