Well, there were also a definite moment in "The Earth King", and whatever the Zutarians say, she was definitely showing some feeling during DoBS, plus a whole bunch of other moments that I could rattle on about forever, but won't.
The thing is that the writers couldn't have too many moments of Katara blatantly and openly liking Aang if they wanted to make the kiss at the end such a special moment. Kataang had to be kept somewhat ambiguous: Aang's feelings were obvious, so Katara's had to be somewhat obscure. That said, I think that her emotions definitely shine through in episodes like:
- The Avatar State
- The Cave of Two Lovers
- The Desert
- The Serpent's Pass
- The Earth King
- The Awakening
- The Headband
- DoBS, part 1
- The Emerald Island Players (for all her talk of it "not being the right time", it is important to note that she never denied having feelings for Aang, and if there is a "wrong time" then that impies that there is also a "right time" at some point in the future.
And of course, our favorite:
- Avatar Aang
It is important to note that there is a fairly real possibility that up until DoBS Katara actually had no idea that Aang had any feelings for her at all. After "The Cave of Two Lovers" she was under the impression that Aang considered kissing her to be only a few steps up from death on his preferences list, and his untimely coldness to her in episodes like "The Desert" and "The Serpent's Pass" probably didn't help things. Indeed, at times during Season 2 Katara seems far more interested in Aang than Aang is in her. If we accept that Katara honestly had no concept of Aang's love for her up until DoBS, a lot of her actions begin to make a lot more sense. After DoBS of course, it was "not the right time", and you can't really blame her for thinking that - the gaang were in fairly desperate straits, and while Sokka might have been willing to take some time off with Suki, it has been established for a while now that Katara is simply not that kind of person.
After Ozai was defeated and Zuko crowned, or course, there was nothing standing in the way of some romancing. The ambiguity was soon abandoned.