Who should lower the body of a female in the grave?

Answer

No, her now ex-husband may not assist. The Nikah ends with death, hence he is a ghair mahram. The mahram males should lower the body of a female in the grave. The first preference is the sons, then the grandsons whether son's sons or daughter's sons. In the absence of these, other mahrams such as uncles and nephews have preference. Only in the absence of mahram males, may ghair mahrams attend to the burial.