Indeed, the Duchess of Cornwall frequently (though not systematically) wears these earrings with her diamond snake necklace. She owned the necklace and the earrings before her wedding with the Prince of Wales.
She notably wore these earrings for her wedding with the Prince of Wales in April 2005:
She also wore these earrings (and the snake necklace) with the Delhi Durbar Tiara in 2005, for the State Visit of the King of Norway:
I guess the earrings must be a family heirloom (either from the Shand or from the Parker-Bowles family), because Camilla's daughter, Laura Parker-Bowles, wore her mother's earrings for her own wedding to Harry Lopes in May 2006. This is the best picture I have of these earrings: