Thanks Janet.

Hans Nadelhoffer https://books.google.com.au/books?id=xnKpjh1gkqgC&pg=PA253&lpg=PA253&dq=Queen+Isabella+II+emeralds&source=bl&ots=MqfJQcPhV3&sig=ACfU3U0Mc_eVqMZNeKLvRhS46WkTf1fVHw&hl=en&sa=X&ved=2ahUKEwis0_KCr5blAhUw6XMBHR-yADoQ6AEwGnoECAoQAQ#v=onepage&q=Queen%20Isabella%20II%20emeralds&f=false stated that the cross had been given by Queen Isabella II to Empress Eugenie. (In the published edition I have -- 2007 edition -- it is on page 253)

But! In Van Cleef & Arpels. Treasures and Legends Vincent Meylan cites the memoirs of Princess von Metternich which recorded that King Francisco of Spain (husband of Isabella II) gave the cross to Empress Eugenie in June 1867.

Vincent Meylan's research, as published in Christie's. The Jewellery archives revealed, shows that the emeralds in Queen Ena's necklace were left to her by Empress Eugenie after the latter's death and were not a wedding present. Vincent Meylan convincingly debunks the claim that those emeralds came from the Empress' emerald tiara.