I have no idea who she is. According to Wikipedia, the title of Duke of Kent was inactive and it would stay so until Queen Victoria's father, Edward, became Duke. His predecessor, Henry Grey died in 1740 and had no daughter who married a Wadsworth. I also cannot find this person in thepeerage that often lists Ladies by their maiden names.
From jeannedepompadour.blogspot.com/2012/03/turquerie-in-portrait-paintings; reduced temperature and shifted toward green tint in an effort to turn the dress from yellow towards white and bring green foliage and blue sky into the background.