This portrait was painted by the incomparable Madame Elisabeth Vigee Lebrun who, incidentally, was Marie Antoinette's official portraitist. The subject is the Baroness Crussol, wife of Henri-Charles-Emmanuel de Crussol-Florensac, lieutenant general of the armies of the King of France.
The Baroness holds a book of opera music, opened to a score by Christoph Willibald Gluck who, incidentally, was Marie Antoinette's preferred composer. (Read entire post.)
I believe this is the same Madame de Crussol who accompanied Madame Elisabeth to the guillotine. (More HERE.)
.