But what about the $13k that the family invested based upon the pre-approval? (again, of course, if it's true that the cemetery did so)
Fire the employee, have written standards of what can be placed in the cemetery, buy the family a plot elsewhere or reimburse them for their utterly insane choice of headstone.
If the family spent 13k on that monstrosity they have more money than brains or taste. A cemetary is sacred ground and that doesn’t belong. Put it in the backyard if it means something to you but don’t impose it on the rest of the community looking for a sacred, dignified place to bury their loved ones.