>>725496454
The text written by Nojima establishing that:

That you've a version of Rinoa that is trapped in the Time Compressed World, who finds herself in a recreation of the room where she first fell in love with Squall reliving the past, a past she can't remember quiet well. And she doesn't know how long she has been there, thinking it could have been forever of just a moment.

This text alone explain how Rinoa can live so long and how Rinoa can act differently since she can't remember her own past.

For you to ignore this you need to pretend that the prologue cinematic doesn't exist, the ending cinematic doesn't exist, and that the room where Rinoa first fell in love with Squall was recreated in the Time Compressed World by Ultimecia just for shit and giggles.