The Norton Simon museum has this portrait (On the left) in their collection and it’s described as:
Portrait of a Lady, first half, 18th century French School
It looks very similar to this prepatory study (On the right) done in 1750 by
of Madame Adelaide, one of the daughters of Louis XV and Marie Leszczyńska. I’m guessing it’s a copy of that drawing, since the women in both look almost identical, with a few minor differences that could probably be put down to different artists.