Her maiden name was probably Elizabeth Letitia Winn whose article in thepeerage is here.
From Wikimedia.
Lady Strickland's bodice is boldly decorated with three large contrasting bows that match her under-dress in this 1751 Devis portrait. She appears to have her sheer apron caught up in her left arm. She appears to be wearing a robe à l'anglaise.
Keywords: 1751, Devis, Elizabeth Winn, Elizabeth Strickland, Lady Strickland, British, straight coiffure, ribboned hat, jacket, lace, bodice, square neckline, bows, elbow length close sleeves, engageantes, vee waistline, apron, full skirt