I was meaning more the bottom stone in her diamond necklace. It's not dangling like a regular pendant would but the pendant could be clasped to a dia...

And here's another with the crown and with the same necklace again. Would the bottom pendant diamond be the right size to be the Carlotta diamond at ...

Here's one of the other paintings with the crown:

Yes, that's the crown. I found another painting of her wearing the same crown by a different painter, but no information on the crown itself.