This is part of the transcript from the episode Jet that I went over after rewatching Avatar:
Katara: Why do boys always think someone has to be the leader? I bet you wouldn't be so bossy if you kissed a girl.
Sokka: I-I've kissed a girl; you just haven't met her.
Katara: Who? Gran-gran? I've met Gran-gran.
Sokka: No, besides Gran-gran.
Katara knows Suki so it isn't Suki. So when Sokka says "You just haven't met her", he implies that it is a person that Katara least expects - HERSELF!
I rest my case.
Edited 2 total times.