You've got it,
Nerwen - Thuringwethil it is! Take over, please.
(Explanation for
Galadriel55 about the mortality question: Most sources I've consulted seem to assume Thuringwethil was some sort of corrupted Maia, and as such, she would of course be immortal; but Tolkien himself never really tells us what kind of being she was, only that she acted as Sauron's messenger and took the form of a vampire bat, so it's at least conceivable she was some other creature - maybe a real bat corrupted and enhanced by sorcery, or something like Beorn's dark cousin six millennia removed

. Sorry for the confusion!)