Stephanie is currently the Countess of Polignac I believe so perhaps it is possible for what you said
Well, unlike her nephew and niece, who are styled Jacques, marquis des Baux and Gabriella, comtesse de Carladès, indicating holders of unique (courtesy) titles (the titles are really held by their father), Stéphanie is not
the Countess of Polignac, as she is just an agnatic descendant of a junior line of the Dukes of Polignac. Her 3 x great grandfather, comte Melchior de Polignac, was a younger son of the 1st Duke of Polignac, the husband of Marie-Antoinette's favourite. He was an émigré who died in Russia. (Catherine the Great granted him an estate in Ukraina.)
If she hadn't already been princesse Stéphanie de Monaco (and not Stéphanie, princesse de Monaco), comtesse de Polignac, she would have been comtesse Stéphanie de Polignac, according to the French custom of
déclinaison des tîtres.