Her German-language Wikipedia article is here. Her article in thepeerage is here.
From Wikimedia; intrusions from frame left intact.
Elisabeth Christine Ulrike’s dress is decorated with bows on her sleeves and en échelle on what appears to be her split bodice.
Keywords: 1765, Ziesenis, Elisabeth Christine Ulrike von Braunschweig-Wolfenbüttel, von Braunschweig-Wolfenbüttel family, Hohenzollern family, Duchess, Crown Princess, German, straight coiffure, neck band, ruffles, chemise, modesty piece, elbow length virago sleeves, bows, arm bands, lace cuffs, split bodice, strap sleeves, bows en échelle, vee waistline, full skirt, robes