This feminization of Anthony, like other early French forms, such as Babette and Nanette, is not heard as often as it once was, but it could be time for a reappraisal of this delicate Gallic choice.
The name is most familiar via the ill-fated Marie Antoinette, wife of King Louis XVI during the French Revolution. Antoinette Giry is a character in Phantom of the Opera. And the theatrical Tony awards were named for theatrical actress and director Antoinette Perry (born Mary Antoinette).
Other options: Antonia and Antonella.