Lady Selina had already joined the Methodist movement when this portrait was painted in 1745. She was born in 1707 and lived until 1791. Her Wikipedia article is here.
Their costumes are retro by a century. Their costumes are also somber, perhaps reflecting religious views.
Keywords: 1745, Soldi, Selina Shirley, Selina Huntingdon, Countess, British, curly coiffure, scarf, vee décolletage, elbow length puffed over-sleeves, elbow length puffed under-sleeves, necklace, earrings, theatrical dress