Probably one of the numerous successor sorceresses we see during time compression. Just a hunch though.

Really though, there are so many plot points that weren't explained or poorly explained that it's barely worth thinking about. It's fun to theories and all but ultimately most of this [img]/xxx.gif[/img][img]/xxx.gif[/img][img]/xxx.gif[/img][img]/xxx.gif[/img] doesn't have an answer because FFVIII's story is a steaming load of Deus Ex Machina crap.