Most likely, all major gala pieces of jewellery remain with the monarch, the ones with the "crown" and the rest private.
It is nice to see Camilla with this tiara. But I do not understand her pairings. It is always a "fruit salad" to me. Considering they have full "parures" of colours, several in fact, I whish they wore more of it. I hoped this was worn by Catherine, but maybe it is smart if Camilla is the first one to wear this one, and next time the on Meghan wore. To state her status as Queen and "owner" of the jewellery. Next time it will not be controversial if Catherine want to borrow a tiara, even Meghans bridal tiara.
I wish instead Camilla wore this piece, with emerald earrings, emerald brooch and the "lost" emerald necklace from the Queen mother.