The estate of X would go to their great-grandmother, A, as she is the closest surviving relative.
The most correct answer pertaining to X's intestate estate, when X dies and is survived only by her great-grandmother A, is that A, as the closest living relative, would generally be entitled to inherit X's estate. The specific distribution of the estate would depend on the laws of the jurisdiction where X resided at the time of her death. These laws typically have a set order of priority for inheritance when a person dies without a will (intestate). In many jurisdictions, the closest living relatives, such as children, parents, siblings, grandparents, or great-grandparents, would have priority in inheriting the intestate estate. Therefore, in this case, as the great-grandmother is the closest living relative, she would usually be entitled to inherit X's estate.
