There was a list of gifts to the royal family last year. I cannot find it online, but it was printed in an online newspaper. The Kuwaiti Amir had presented jewellery to several royal ladies during his state visit, possibly also the Princess Royal.
The Princess Royal rarely wears grand necklaces.
I seem to recall the Princess Royal wore a modern necklace also for the state banquet when the King of Saudi-Arabia paid a state visit in Oct 2007. She was briefly pictured inside a car, though no clear picture. I cannot remember the stone, was it perhaps a sapphire necklace? It is very likely she received this necklace from the Saudi King on a previous visit.
--Previous Message-- : Princess Anne owns a modern ruby and diamond : "twist" necklace which I have only : seen a picture of her wearing once before, : at the SpecSavers Gala in Oct. 2012. : : The necklace has reappeared on the Princess : Royal at the UK Fashion and Textile Awards. : She is wearing it with a diamond and ruby : brooch which looks like it may belong to the : same demi-parure as the necklace. : : She is wearing diamond and ruby earring : which I don't recognize. : : I wonder if there are better pictures : available. :