I cannot find anything, other than this portrait, about her.
From 18thcenturylove.tumblr.com/post/23762480190/marquise-de-grecourt-nee-de-la-fresnaye-by.
The Marquise wears late pre-Revolutionary style with a wide curly coiffure under an expansive cap and a banded fichu over a colorful dress.
Keywords: Mosnier, Marquise, long bouffant coiffure, cap, fichu, long tight sleeves, waist band, earrings