Probably jumping to conclusions here but what if she's been tainted by Crota? It would explain the way she looks etc and how else could she spend so long down their undetected.... Also bungie mention what we've seen so far is just one of crota's forms! In a way it kinda makes sense, his biggest threat are the guardians on earth. Once were dead, earth and the traveler is theirs for the taking. So naturally why fight your enemies on their terms on ground they know when you can present them with an opportunity they can't resist! Kill a god and become a hero! As said before its all just assumptions on my part but it just screams "TRAP!!!" To me.