At 0:56 in the video of the Queen's speech is a woman that has been identified by Estella_NYC on The Queen's Jewel Vault as Lady Charlotte Santo Domingo nee Wellesley, youngest daughter of the Duke of Wellington. I don't recognize the tiara she's wearing. I don't think it's the Wellington tiara, what do you guys think?
Update Estella_NYC identified the tiara too! It's Princess Frederic of Prussia's tiara worn by Lady Charlotte's cousin, Princess Florence of Prussia when she married James Tollemache in 2014.