Just to recap: despite her protestations to the contrary, there is no such person named Lady Grania Mary Mountbatten, who claims to be the daughter of the late Lady Iris Mountbatten and the late Hamilton O'Malley. Lady Iris and Hamilton O'Malley were married in 1941, and separated shortly afterward. They were divorced in 1946. "Lady Grania" claims she was born on July 31, 1946 in France. Her life story is completely fabricated. It also seems she borrowed some of the genealogical details from Hamilton O'Malley's only daughter, Grania Mary O'Mally, who was born July 31, 1950, the third of five children by his second wife, Eleanor "Sadie" O'Kelly.
Hamilton and Sadie also had four sons: Charles Patrick (1947), Patrick Peter (1949), Dermot Raymond (1951) and an unnamed son, who was born in 1959. This information can be found in Burke's Irish Family Records, which was published in 1976.
Thus, "Lady Grania" has pinched family details from the real Grania Mary O'Malley to concoct a complete work of fiction.