Madame Adelaide, shown here in 1756 by Perronneau after Nattier, was one of Louis XV's daughters who did not marry.
(http://www.gogmsite.net/grand-ladies-of-the-eightee/subalbum-madame-adelaide/1756-madame-adelaide-pastel.html)
Wikipedia attributes this painting to Nattier.
"Marie Adélaïde de France, (23 March 1732 in Versailles – 27 February 1800 in Trieste), was a French princess, the fourth daughter and sixth child of King Louis XV of France and his consort, Marie Leszczyńska...."
(https://en.wikipedia.org/wiki/Ad%C3%A9la%C3%AFde_of_France_(1732%E2%80%931800))
However at least one other site says this is by a follower of Jean-baptiste Peronneau 1715-1783
and is a portrait of a noblewoman, thought to be Madame de Pompadour.