Rinoa, unbeknownst even to herself, is a descendant of the great god Hyne, and therefore has the innate ability to be a sorceress. As the great epic that is FFVIII unravels, we find out that Rinoa is the sorceress Ultimecia from the future. Having lost her Knight, she became corrupted by her own power and more or less destroyed the world. She becomes bitter and twisted and so tainted by her own magic that her physical self morphs into that of a hideous beast.
Wanting to return to the time when she was young and beautiful, and had her lover Squall Leonhart by her side, she creates Time Kompression; a state of reality where all levels of time 'past, present & future' are combined. Destined to be slain by the man she loves, Ultimecia is vanquished and Time Kompression is reversed, thus sparing her younger self, Rinoa Heartilly from ever enduring such a fate again.
As Time is once again righted, Rinoa Heartilly lives happily ever after with Squall Leonhart.
... Rinoa Heartilly is not a copy in any way, shape or form of Final Fantasy VII's Tifa Lockhart.