Soul Eater, Who is she really?

Stein's "Daughter" Joins DWMA confusing most students on who, or what she was, since a lot of the students who could see souls, didn't even feel her presence, and they can't see her soul, almost as if she wasn't even there. She was raised by Stein but she doesn't look or act anything like him, she doesn't have a last name so no one knows who she really is, but then again she doesn't even know who she is, her Weapon Partner might know a little more than she does, but other than that, only Lord Death and a few teachers know who she really is, but they won't tell. SoulXOC