That's a pity, but this video clip is from the pre-wedding ball for Princess Caroline and Philippe Junot, and Princess Grace is definitely wearing her own Van Cleef & Arpels tiara (which as far as I know was never worn as 'collier').
Picture from the occasion with Princess Caroline wearing her mother's diamond 'wave' tiara and Princess Grace in her new Van Cleef & Arpels tiara:
--Previous Message-- : It is hard to say, but when the stories are : true about the cold war between the Château : de Marchais (Charlotte) and the Palais : Princier (Gracia) then your theory of : Princess Gracia wearing her fringe collier : as a diadem sounds more plausible. : : The "Sissi" entrance was really : overpowering but I am not sure the diadem : was real. The glitz and glam coming from : that diadem was a bit different, less : "depth" and less sparkle than real : diamonds would do in my imagination. : : It has never struck me, but now I think : about it: Princess Gracia really had : fantastic diadem-hair. In that department : she easily was on the same level as Queen : Silvia. Also funny to know that the : wonderful Château de Marchais (around 60 km : from the Belgian-French border) and its : domains, still privately owned by the : Prince, is six to seven times bigger than : the whole principality itself. :