That last comment should read that most fringe tiaras are convertible to necklaces. Also according to the Royal Collections Trust website (part of the Royal Household) the tiara worn here by Mary is the Queen Adelaide tiara.
DIAMOND GARLAND TIARA MADE BY CARTIER In 1927 Queen Victoria Eugenia of Spain ordered a tiara with arching laurel wreaths interwined around two horizontal garlands of leaves, a thematic invention which, considering the predominant styly of art deco at
The Londonderry Tiara (top) worn by Theresa, Marchioness of Londonderry (left) with enormous pearl spikes and (right) with inset crown frame and upright cross, probably at the Devon-shire House Costume Ball of 1897 where her jewelry dazzled everyone.
Made in this tiara is designed as a series of graduated open work garlands of floral and foliate motifs, featuring seven natural saltwater pearls. The floral and foliate elements are millegrain-set with rose, cushion-shaped and circular-cut diamonds.