In the 1760s the earl was appointed Ambassador to France and was accompanied by his wife, whose portrait was painted in Paris by Alexander Roslin.

From 1768 until her death, the countess was a Lady of the Bedchamber to Charlotte of Mecklenburg-Strelitz, queen consort of King George III of the United Kingdom.

[2] The earl and countess were the subject of at least two caricatures created by the political cartoonist James Gillray.

One of these, "Dame rat, and her poor little ones", published in 1782, shows Isabella and her husband in the company of Charles James Fox.

[3] She died, aged 56, after a visit to their grandson at Forde's Farm, Thames Ditton, where she was taken ill. Horace Walpole, who was related to the earl and a correspondent of the countess, said, "Lord Hertford's loss is beyond measure.