The emerald necklace definitely sits in a rather strange way around the neck - something about it is off-key as if it was altered, or was worn in a wrong way. As it is, it produces an unfortunate 'clothes-pegs on a washing line' effect.
Regarding the hairdo, it's teased and whipped and sprayed into volume and width to balance the wide Boucheron tiara... and I don't like it one bit.
It's rather like 1977 Farrah Fawcett hair minus a few inches, quite wrong for Camilla and disctracting from the jewelry instead of complimenting it. It's just not a tiara hairdo to begin with.
A minor point: The rather romantic diamond earrings and the stark design of the emerald necklace are not a good match.