So I just saw someone cosplaying as Sheik on Facebook, and she was carrying Sheik's harp. But the person posting the photo - a mod from a Zelda Facebook page - referred to it as the Goddess Harp specifically.
It would make sense if Sheik's harp is the Goddess Harp, because that would imply that it's handed down to Zelda in the same way that, say, it will always be Link who gets the Master Sword. But is there anything canonical to confirm this either way?