She obtained a divorce by Act of Parliament from her first husband (who was also her cousin), Charles Daly of Loughrea, in order to marry Lord Kerry.
Nonetheless, the inscription which he had placed on her tomb in Westminster Abbey makes it clear that he never regretted marrying her: it states that for 31 years she made him the happiest of mankind, due to her "charity, benevolence, truth, sincerity, meekness and simplicity".
Others who knew the couple took a more jaundiced view: Horace Walpole called Lord Kerry "a simple young Irish peer that has married an elderly Irishwoman, who was divorced on his account, and wasted a vast estate on the idlest ostentation".
The Earl's cousin, whose son was his heir, William Petty, 2nd Earl of Shelburne wrote uncharitably that "he fell in love with a married lady twenty years older than himself, the daughter of an eminent Roman Catholic lawyer, and she having obtained a divorce, married her; [she was] an extraordinarily vain person.
Having their way to fight up into good society, and having no children, they sold every acre of land that had been in our family since Henry II's time".