I can find no biographical information about her.
The shimmering colors suggest this is a dupioni fabric dress. The colors are striking, particularly the violet plumed hat and the white ruff and black lace wrap. This dress probably gets attention.
Keywords: 1784, Vigée-Lebrun, Comtesse de Cérès, Countess, French, curly coiffure, feathered hat, ruff, cape, long close sleeves, forward-back flared cuffs, full skirt, wrap, lace