Great! Thank you, Gert-Jan! These pear-shaped (sapphire?) earrings look different than the sapphire and diamond cluster earrings regularly worn by the Duchess of Cambridge. And the pendant seems to be matching with the earrings, thus forming a set.
Just a regret: isn't the Duchess of Cambridge sponsor (not sure if it is the right word in English, sorry) of one or several military unit(s)? If she is, she could have worn their badge pinned on her coat, that would have been very appropriate in such an occasion.
Here are a few other pictures, from Zimbio:
(Source: Chris Jackson & WPA Pool/Getty Images Europe, via Zimbio.com)