From Wikimedia. This is the largest version I can find. Also posted to Varvara Petrovna Sheremeteva’s new Subalbum here.
The coiffure, with somewhat visible large curls behind, dates this to the 1770s. She wears a lace-trimmed hooded over-garment.
Keywords: Varvara Sheremetev, Sheremetev family, Razumovsky family, Countess, Russian, straight large curl coiffure, choker neck band, lace-trimmed hooded cape