Her article in thepeerage is here. She died with out issue and the title disappeared.
The title suggests it was assigned by an auction house such as Christie’s. From meisterdrucke.uk/artist/Jean-Étienne-Liotard.html; doubled size. Also posted to the Reign of Louis XV - 1715 to 1774 Album here.
Lady Grace’s dress is sumptuous yet simple, enhanced by lavish engageantes and a few well-placed bows.
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