[He blinks, trying to process this. The alternate versions of people he's met so far have just been blips - different versions that have "reset" to their original person. But this Katara was so radical and different... That this Sokka had met her in the past, too... It made Aang acknowledge that creeping fear that this other Katara had her own individual life.]

I can't believe this. That long ago? Does that mean... Do you know what happened to her? What made her so- so different?