I don't know which picture you are talking about, Tamara. Probably one I haven't seen sofar.
So I added Princess Margaretha of Sweden (sister of the current King) to the comparison panel. She had worn the Kedive at the 18th birthday of another Princess Margrethe of Denmark. Versions of the name really run in the family! I thought that another older, blurry black-and-white pic was best to compare the impression.
Imo the outline of the mystery tiara fits best with the Khedive. But the Boucheron is more open, see-through, wich also fit with the mystery tiara.