Likely a mid-1800s souvenir created for travelers visiting France, after historical figures of the Louis XVI and Marie-Antoinette era - perhaps originally sold at or near Versailles Palace, this is a hand painted portrait of a teen or a young woman, girl, her costume puts her squarely into the c.1770s. The outer frame mount, convex cover glass and pin back brooch suggests it was made a century later. The brooch is 2" in diameter. All measurements noted on the photos.
Very good to excellent condition throughout, I see no flaws to report. The facing mount seems to look like copper, but no tarnish. I did not test. It is possible it is a low karat rose gold facing or plate. Backing is brass. No flaws to note. Original as you see it. That tiny face is just 1/2", chin to hairline.