Harriet, Countess Gower and her Daughter, Elizabeth Georgiana, later Duchess Of Argyll after Sir Thomas Lawrence (auctioned)
Based on the birth date of Elizabeth Georgina, later Duchess of Argyll, of 1824 this portrait would date to around 1826. The year 1826 is consistent with Duchess Harriet's dress. Elizabeth Georgina's summary in thepeerage.com is here. Elizabeth Georgina's oldest son, John Marquis of Lorne, married Queen Victoria's daughter Princess Louise.