The necklace Her Serene Highness wore is by Repossi from the Brevis collection. It looks a lot like the Lorenz Baumer tiara but it's completely unrelated.
https://theroyalcouturier.com/2020/09/princess-charlene-dazzles-in-jenny-packham-at-the-monte-carlo-gala-for-planetary-health
Her diamond...