Unless, of course, instead of Squall & Co rescue Rinoa in Estar, she be frozen in that machine for many generations.
Unlikely... but ok.

But get this, Rinoa and Sorceress Ultimecia are nothing alike, even the wings are not the same as Rinoa ''not to mention the color!''

And Ultimecia's Final Form... You better not tell me that cute little Rinoa can turn into this monster.

It makes no sence, if it really were Rinoa, why did she said to Squall ''Who's there, Get out!'', if it were Rinoa, she would know Squall and not ''Who's there.''
When you challenge Ultimecia, she says SeeD six time, Rinoa isn't a SeeD, and Irvine isn't quite a SeeD either.
Why go against your friends? (Felt Betrayed? no.)

The R=U theory doesn't stand on it's feet.

And please don't talk about this, there are better theory that makes more sense and are more 'provable' than this... (Except Time-Travelling...don't even start.)