I'm betting this is after (aprés) a painting by Jean-Baptiste Greuze (1725-1805, Paris). Doesn't it look like it to you? Or perhaps it just looks so much like one in particular, "La Petite Soeur, a contemplative young girl, oil on canvas, 40 x 32.5 cm, framed", which original sold through Dorotheum at $92,000 plus hammer in 2011 (look online for it to see for yourself). That said, it's a very charming miniature, and more likely the type made as a Grand Tour souvenir, after the paintings seen and loved by the travelers. If I'm right, and I think I am, it would have been a thrilling souvenir of someone's visit to perhaps the Louvre, Paris. There are really 2 types of miniatures: those done of a person, directly, artist and sitting actual person - one of a kind, and those done after the works of another artist. Of those, 2 types: some souvenir in nature and some political in nature, such as the multiples Napoleon and Josephine had done and passed out freely, creating their fame. This would be the souvenir type. Dating early to mid-1800s, it remains in its original frame, and is on thin wafer, painting is in gouache.
Very good to excellent condition for age and type. There is a signature to the lower right, but it is not readable. It looks very much like a Greuze subject, though that painting is only the adult, not the child, so perhaps a bit of a play in souvenir and portrait. Curious and thrilling, this one. Easel back, the tabs have been lost and it holds together with pins now. Measurements are noted on photos. No chips or cracks, no hairlines. Cover glass in place. She's from my personal collection.