This portrait’s full title is Archduchess Maria Antonia of Austria, the later Queen Marie Antoinette of France.
The formality of the portrait and it’s title is due to the fact that it was a royal teaser — in 1769, Joseph Ducreux traveled to Vienna to paint Maria Antonia, who was planned to mary Louis XVI of France. Ducreux’s portrait would have been the first glimpse Louis XVI would have had of his wife to be. The portrait was a success, and Ducreux was made a baron and premier peintre de la reine (First Painter to the Queen).
Reed Enger, "Portrait of Marie Antoinette," in Obelisk Art History, Published April 11, 2016; last modified May 19, 2021, http://arthistoryproject.com/artists/joseph-ducreux/portrait-of-marie-antoinette/.