She did not wanna be old. She freaked out when she turned 18 and again when she turned 19. Considering this, and the fact that she always says 'me me me' --and the fact that Edward can't 'hear' her, which means she really is thoughtless-- I'd say that it sounds like she figured it out and decided that she really didn't want to grow up and be a real girl. Or something.

I've read vampire books where the herione basically says 'come and get me, big boy' after a short time, there is a reason for it. Not OMG TRU LURV, HURHUR. *facepalm*