Complex sentence: She is the second daughter of Roderick Francis Arthur Balfour, 5th Earl of Balfour and Lady Tessa Mary Isabel Fitzalan-Howard, and a niece of the Duke of Norfolk.
Split into simpler sentences: She is the second daughter of Roderick Balfour, 5th Earl of Balfour and Lady Tessa Fitzalan-Howard. Balfour is a niece of the Duke of Norfolk.