I am guessing she is Maria Theresia before she assumed the throne in 1740 based on the relative lack of jewelry and lack of regalia found in her later portraits.
From pinterest.com/nataliausastova/portrait-xviii/.
Her bodice has a rigid center panel or a stomacher covered in matching fabric. The under-sleeves are a carry over from the 1600s.
Keywords: Empress Maria Theresia, Maria Theresia Walburga Amalia Christina von Habsburg, Erzherzogin von Österreich und Königin u. a. von Ungarn mit Kroatien und Böhmen, römisch-deutschen Kaiserin, Mária Terézia magyar királynő, Maria Teresa d'Austria, duchessa regnante di Parma e Piacenza, duchessa regnante di Milano e Mantova, císařovna Marie Terezie, Archduchess, Empress, Habsburg family, long curly coiffure, floral headdress, earrings, chemise, modesty piece, off shoulder scoop neckline, three quarter length full under-sleeves, lace cuffs, fitted bodice, off shoulder vee neckline, brooch, elbow length notched full over-sleeves, clasps, girdle, vee waistline, full skirt, wrap