Quote Originally Posted by champagne supernova View Post
2) Rinoa in the game is a upbeat, light-hearted, friendly girl. Ultimecia is an absolute loner. What evidence IN THE GAME or RELEVANT SUPPORTING MATERIALS suggests that such a change would occur?
None whatsoever, with the possible exception of that scene where Rinoa frets about the possibility that she might somehow become "the world's enemy", and Squall silently vows that he'll be her knight even if that happens. But that's just idle speculation by a pair of frightened teenagers who don't know what the future's going to bring.

Rinoa had a vision about the future, and that was her dream of Squall getting lost and her running around the world trying to find him. This eventually happens, when Squall's isolated from the others during their escape from the future, though compressed time, at the game's end. She never had any dreams or visions about becoming a world-destroying evil force, nor was there a glimmer of recognition or familiarity when she came face-to-face with Ultimecia.
3) Rinoa and Ultimecia do not look the same. Even with the constant use of dark magic, it would seem unlikely that Rinoa's entire facial structure would change to become Ultimecia's. Especially seeing that the age difference is not that large, and therefore Rinoa would not have been casting dark magic for a large portion of her life.
To be fair, it's hard to say just how old Ultimecia might be. She's got a rather impressive figure, from what we can see of it (which is quite a lot really), but that doesn't necessarily mean she's youthful, merely well-preserved. Smooth skin could even be a side-effect, one of the mutations triggered by magic abuse. She's got completely grey hair, after all. Adel's proof that sorceresses can indeed mutate into something hideously inhuman, given enough time and dark magic. But again, nothing overtly suggests that anything similar happening to Rinoa.