Thanks, Beth and Nellie. I do not have more information about this necklace.
Regarding the earrings: the inner diamond drops seem to be removable, as Princess Alexandra was seen with these earrings bearing sapphire drops, matching with the Princess sapphire necklace:
July 18, 1974 - London, England, U.K. - Singer Sammy Davis Jr. accompanied by his wife Altovise greet Princess Alexandra, at his charity caberet show at the Grosvenor House. (Credit Image: Keystone Pictures USA)