Although his father did not approve, in 1843 she married the future Duke of Marlborough and they became the parents of five sons and six daughters. Like her mother at Wynyard, Duchess Fanny ruled Blenheim with a firm hand and, according to one daughter-in-law, "at the rustle of her silk dress the household trembled".
In 1876 her husband was appointed as Viceroy of Ireland, a post which he did not particularly wanted, and she accompanied him to Dublin. During the Marlborough's third year in the Viceregal Lodge there was an exceptionally wet summer, in which the potato crop again failed, the grain would not ripen and the turf could not be dried.
Duchess Fanny, described by her grandson Winston as: "a woman of exceptional capacity, energy and decision", threw herself into the work of famine relief, and as a result of her endeavours she was able to raise œ135,000/-. Furthermore, the administration of the fund and the provision of food, clothing and fuel, was entirely free from sectarian or party influence, Roman Catholics and Protestants being equally represented on the Committee.
She may have adored her third son, Lord Randolph, she cared little for her grandson, Winston. When Consuelo, wife of her grandson, came to visit her for the first time, she described Duchess Fanny as having "large prominent eyes, and aquiline nose, and a God-and-my-right conception of life, and left her account of the meeting: "
"The Duchess was seated in an armchair in the drawing-room of her house at the corner of Grosvenor Square where she had lived since her widowhood. Dressed in mourning with a little lace cap on her head and an ear-trumpet in her hand, she bestowed a welcoming kiss in a manner of a deposed sovereign greeting her successor. After an embarrassing inspection of my person, she informed me that Lord Rosebery had reported favourably on me after our meeting in Madrid. She expressed great interest in our plans and made searching inquiries concerning the manner of life we intended to live, hoping, she said, to see Blenheim restored to its former glories and the prestige of the family upheld.
 "I felt that this little lecture was intended to show me how it behoved me to behave. Then fixing her cold eyes upon me she continued. 'Your first duty is to have a child and it must be a son, because it would be intolerable to have that little upstart Winston become Duke. Are you in the family way?' Feeling utterly crushed by my negligence in not having insured Winston's eclipse and depressed by the responsibilities she had heaped upon me, I was glad to take my leave."
Not long before she died she handed a letter from Queen Victoria, thanking her for her work in raising such a substantial sum for famine relief in Ireland, to her grandson to have it placed in the family archives and told him, "I may seem a useless old woman now, but this letter will show you I was once of some importance and did good in my day." She survived her husband and all her sons.
 

Source: Leo van de Pas