I also think now that she maybe a complete new character and makes Roxas leave the Organization for whatever reason.
Oh, well, ok, Roxas wanted to meet Sora, but for ONE WHOLE YEAR he stayed in the Org! He could have looked for Sora sooner if he would have wanted so
That could be posible, but then why and who made them forget?
Or maybe Xemnas made them all forget about her, maybe she really was the manifestation of the memories he had of Aqua.
Remember when Xigbar mentioned the Room of Awakening? Probably there she was created...
Interviewer: Is the 14th member a new character of the KH Series? It appears as though the character is...a woman?
Nomura: I should bring it up now, that the XIV member is not Namine, since some people believed it to be Namine by seeing the trailer. However it will be explained as to why there's no pillar for this character, as well as why she never appeared in Kingdom Hearts 2.
Nomura stated that it isn´t Namine.
I think it might actually be Aqua´s Nobody, since in the new KH2FM+ scenes we saw Xemnas secret lab and his "old friend" he mentioned.
We all know that the original six org members lead experiments on heartless,etc. So there might be a good chance that they used one of the 3 keybladewielders from BBS and created the first Nobody and kept her in secret? Who knows...