I really can not imagine that. What is the point of keeping historic family jewels when the Queen wears copies? If wearing plastic beads during a State Banquet is no problem, why then not selling all the diamonds, sapphires, rubies and emeralds?
It is really a story in the category 'Broodje Aap' (Sandwich with monkey). That the Queen wore the Württemberg Ornate Pearls & Diamonds Diadem with a thick braid around the base indicates it is the real thing. Why soften the frame while she is apparently wearing a copy? Come on...