Okay, so according to "the Big three" Kingdom Hearts sites, the 14th member is not Namine, but she is important in the one year storyline. Couldn't be Aqua, so must be some sort of new character that is really there for symbolic reasons rather than being an actual member. Either that, or she is simply killed at the end.
Going from the scans, I'd say that she looks pretty creepy too. Probably a younger girl(around Demyx-Roxas age, so 15-18), a warrior maiden type(because the Organization doesn't have enough of those), and someone who would probably fit right in with the "Blah Brigade". No ally of Axel's, Demyx probably wouldn't care for her much either, and she'll probably try to be a friend of Roxas', which is something Axel probably wouldn't tolerate because he's mean. She'd probably be closest to Saix or Xaldin. Maybe even a possible ally of Zexion's(which would be another reason why Axel might not be a fan). Because she is nowhere to be seen in KH2, I'm going to ASSUME that she is indeed killed, but you never know with Kingdom Hearts.
Do I want her to be? Well, I don't know who she is or what's she's like, so right now, I don't care too much either way. For all we know, she could just be a spy for someone else. I don't think anyone is going to know for quite awhile.