She is the great-granddaughter of Consuelo Vanderbilt and the step-sister of Christina Onassis through her father's second marriage to Tina Onassis, former wife of Aristotle Onassis.
Christina Onassis is both the step-sister and the great-granddaughter of Consuelo Vanderbilt via her father's union with Tina Onassis, who was previously married to Aristotle Onassis.