Queen Elizabeth II wore, mostly when she was still Princess Elizabeth/the Duchess of Edinburgh (but also later occasionally), a two-row pearl necklace, made of small pearls. But there was a wider gap between the two rows of this necklace than between the two rows of the necklace she wore yesterday. And the "old" necklace seems to be made of round pearls, whereas "yesterday"'s necklace seems to have several oval pearls.
December 1944: Christmas pantomime at Windsor Castle:
1945: official portraits by Cecil Beaton:
February 1947: on board 'HMS Vanguard', on the way to South Africa:
1947: Honeymoon at Broadlands (and "twin picture" sixty years later, in 2007):