In the thread below Andrew U asked who was the lady sitting in front of Rachel Bowes Lyon, https://mb.boardhost.com/historyroyaljewels/msg/1595956473.html

I found the answer in the list of those sitting in the royal box which Laura M had provided on the RJWMB, which Janet gave us the link to.

She was then Lady Rose Leveson Gower, later Countess Granville. She was one of Queen Elizabeth the Queen Mother's sisters.



I suspect that for the 1937 Coronation Lady Rose wore a tiara belonging to her sister-in-law, the then Countess Granville.

I haven't found a photo of Nina Baring, Countess Granville wearing the tiara, but I did find the following description of a tiara she wore in 1934 at a ball given in honour of the then Princess Juliana of the Netherlands.



I think the description above fits the tiara worn by Lady Rose.