Since obviously people don't usually read the entire 15 post topic before posting, I'll reiterate myself:

1) Rinoa cannot live long enough to become Ultimecia, who lives hundreds of years into the future. And no, crackpot theories involving timetravelling or being frozen down in the Sorceress Memorial doesn't count as anything but crackpot theories.

2) For a breakdown of the whole theory, all it's flaws and supposedly good arguments, please read the Time/Ultimecia Plot FAQ here:

http://www.gamefaqs.com/console/psx/game/197343.html

Please, before coming with more 'arguments' from websites, just at least skim through the Ultimecia section there.