Her parents' marriage was dissolved by an Act of Parliament in 1793, and the following year her mother married William Kerr, 6th Marquess of Lothian, and by him had four additional children.

Lady Louisa married on 9 July 1804, George John Montagu, Viscount Hinchingbrooke, MP for Huntingdonshire.

Together they had two daughters and one son, who would succeed his father in the earldom:[2] In 1818, following the death of her husband, who left her with a large jointure, Louisa moved to the Continent, where she spent many years in the former home of Talleyrand in the Rue de St Florentin in Paris.

She is referred to in a letter written by Thomas Carlyle to his mother on 3 September 1848, in which he describes her as having been: "brisk-talking, friendly and an entertaining character".

Twice a week he used to call for her; and now his horse makes for her house whenever he gets into the region of Grosvenor Square, and does not see or understand the escutcheon that turns me sick as I drive past.