The photo marked G in J-F's post above is definitely of the Countess of Dunmore.
Below is a better image than the one I posted above, though it is not as good as the image J-F posted. Nevertheless I think it is clear that the same two people are the subject of the photos, and the jewels match.
Duke of Atholl and the Countess of Dunmore at the Caledonian Ball, 1952.
Detail showing the tiara