Just to add to that there was a lot of talking in Edeas's house about Squall killing Rinoa, Sorceresses without knights becoming evil, Ultimecia probably doesn't have a knight.
It also can be safely assumed Ultimecia was not given that name as a child, and didn't look like that to begin. Both Edea and Adel look different (presumably due to their powers), I don't see why Rinoa should stay the same.
Buffy Season 6 explains how this can work believably, but if you haven't seen it it still makes sense.
