A little excursus: The Art Deco Tiara was given to Sibilla by her parents when she got married, alas, she didn't wear it on her wedding day as she chose not to wear a tiara. Interestingly, the tiara can be worn in two different settings; Princess Sibilla decided to wear the larger setting for the wedding of Crown Prince Haakon and Crown Princess Mette-Marit of Norway almost exactly ten years ago and the smaller one for the wedding of Princess Alexandra of Sayn-Wittgenstein-Berleburg and Count Jefferson of Pfeil and Klein-Ellguth, one wonders how those two fit their names into those tiny form checkboxes... But back to Sibilla: she is also wearing a Diamond and Ruby Necklace today that must be a favourite of hers as she often wears it for formal events she attends. It was given to her by her parents-in-law, Grand Duke Jean and the late Grand Duchess Joséphine-Charlotte, on her wedding day.
Apparently, Princess Sibilla was not the only one of the extended Grand Ducal Family to attend the wedding festivities - Princess Maria-Anunciata and Princess Marie-Astrid of Liechtenstein were in Potsdam as well. A picture of the two Princesses can be found in the photo gallery of Marianne van Dam; another picture of the lovely sisters is available on Netty's Royalty Page.
Sources: me, Newscom