The brooch is new to me as well, not really the nicest piece in my opinion.
It looks as if it could be a piece of mourning jewellery.
As for the rest of her jewellery - I wonder if the Duchess is playing it safe and not trying to upstage the Queen - well in the media anyway....remember at the State Opening some time ago now when the Princess of Wales chose the State Opening to debut a new hair-do - the hair-do got more press then the Opening.