Thepeerage has nothing about this Arethusa Harland; however a thumbnail geneology is found here.
From bbc.co.; spots removed from background with Photoshop by gogm.
British ladies aligned with French fashion as shown by this extremely simply cut dress adorned with ruffle and modesty piece, presumably from her essential chemise.
Keywords: 1795, Arethusa Vernon Harland, Vernon family, Harland family, British, long straight coiffure, ribbon headdress, scoop décolletage, modesty piece, bertha, long close upper puffed sleeves, waist band, Empire low waistline, close skirt, earrings