According to Gazette-Drouot.com, she was a Countess. The Google translation includes this "...miniature according to the commentator the Great Exhibition of 1906 when she appeared. Listed since 1905 under the title of Countess Helfinger born O' Dunne, this portrait represents Marianne O' Dunne, daughter of Jacques-Bernard O' Dunne (Kilkenny, Ireland, 1714- Paris, 1794), Ambassador of France in 1780 -1785 in Lisbon where he lived in great style. He obtained from King Louis XVI the sum of 220,000 pounds for both his return to France in 1785 to serve as the release of his debts. The young woman married Lorrain Jean-Frédéric Helflinger (Helfflinger) (Saint-Avold, to 1749-1815), who was secretary of embassy in Germany and responsible for business in Portugal in 1780-1787. Appointed by the King of France in Valais resident remained there during the Revolution (1788-1797) and was responsible for business ?? Dresden (1798-1 800), and Minister of France in Hesse-Darmstadt (1801-1812). The portrait dates from around 1785 and shows the background of the park, in subtle shades of white, pink and gray, tinted red carnation in her pale pink blouse, green sleeves and ribbons in her hair adorned with a veil and flowers."
From artnet.com/artists/pierre-adolphe-hall/past-auction-results; image size doubled.