No idea, but since you're the one who's asking, it's probably Tar-Miriel
Seriously, the only thing that rings a bell is sheep = Erendis (or possibly Ancalime), but I'm not sure how the rest of the riddle fits either. With all of Númenor, including their graves, being submerged, you can I suppose say they now dwell in water; the 'shadow of a shadow' remains puzzling.