I believe that most of Princess Alice and Princess Elena's jewels were not in Greece during the occupation!

We know that Princess Alice's Aquamarine Tiara was in a bank vault in London when Prince Phillip broke it up for the engagement ring and bracelet. Princess Alice went through some serious hardships during the war, and had she had her jewels, I'm sure they would have been sold. On a similar note, I haven't ever found the original source that says that Princess Alice gave her Meander Tiara as a wedding gift to the Queen, and a new theory of mine is that she kept it with her (wearing it at the wedding too) until she came to live with the Queen and Duke in 1967, around the same time Princess Anne started wearing the Meander Tiara.

By the time of the occupation, Princess Elena had two main Tiaras left: the Vladimir Fringe and Queen Olga's Ruby Parure, which were both worn by Princess Olga and Princess Elisabeth during the Yugoslavian State Visit to Germany in June 1939, and I thought that both Tiaras were with both daughters respectively for the duration of the war, but it seems Princess Elena wore the Rubies in Italy in July 1939, and now I'm not sure if the jewels were with her in Greece for the duration of the Nazi occupation.