She came from Ireland and first married the Duke of Hamilton in 1752 and the Marquess of Lorne and later Duke of Argyll, one of the Campbells in a famous feud with the MacDonalds, in 1759 after the death of the first husband. She was a Lady of the Bedchamber to Queen Charlotte and George III created her a Baroness in her own right. Her Wikipedia article is here.

Elizabeth Gunning (1733–1790), Duchess of Hamilton (Later Duchess of Argyll) wearing a dress with a stomacher by Gavin Hamilton (National Galleries of Scotland - Edinburgh UK)
