Fox-Strangways was the childhood object of affection of her first cousin and future Whig statesman Charles James Fox (1749–1806), who in 1760 when a schoolboy at Eton College, composed a prize-winning Latin verse describing a pigeon he found to deliver his love-letters to her "to please both Venus its mistress and him".

[4] Fox-Strangways met Irish actor William O'Brien, of David Garrick’s Drury Lane Theatre, in late 1760 to early 1761 when he was employed as a salaried elocution teacher at Holland House.

When her family and relations found out about the secret marriage, her father was determined to cut all communications and her mother unhappily forgave her, but her sisters continued to stay in contact.

[8] The writer and politician Horace Walpole commented of the match "even a footman were preferable — the publicity of the hero's profession perpetuates the mortification".

However, the two struggled to find a source of income to sustain their standard of living in America, even with Lord Holland's allowance of £400 a year, as O'Brien was said to have "expensive taste".