Thank you Malluu. You have put forward a very interesting idea, which is possible as the design of the two tiaras is similar.
If only someone had access to the 1946 Christie's catalogue so that a complete description of the tiaras could be obtained - and hopefully some photos. I have done searches on British and Australian newspapers but the only additional information I could find is that the sapphire necklace given to QA by the Czar and Czarina for her 25th wedding anniversary was purchased by a Colonel Drayson.
Until we have additional information, I suspect the composition of the tiara Queen Alexandra wore for the wedding of her daughter cannot be established. Press reports clearly state that she had a sapphire and diamond tiara but I have never found photos which would conclusively identify such a tiara.