Killing Aang would ruin the show. There are no airbenders left. That would mess up the cycle. Some people would want to ruin the show just for a ship?

(I hope you guys know i'm joking with this..)

Avrura, your comment about the kissing stood out to me.

"It's the main reason why she never kissed him on his lips, she wants it that way, she's a friend."

That doesn't prove anything. Just because she hasn't kissed him on the lips doesn't mean she doesn't love him. It could mean a lot of things, and it doesn't automatically imply that she doesn't love him. I think all she meant by the kisses were just what they were--innocent little kisses on the cheek. I think they got their points across perfectly well.

Let's go over the three of them. The first one, I thought, probably meant the most when it comes to Kataang. Aang gave Katara her necklace back and she started acting all innocent and appreciative, which to me was pretty obvious flirting. Then she quickly gave him the kiss. The second one took place right before the Gaang split up, basically as a sweet goodbye gesture. The third one was after the dance party in The Headband, and to me that had two meanings. 1) She was proud of him for helping the fire nation kids feel better and relieved some of their stress. And 2) she was thinking back to the time they had dancing, which contained a TON of Kataang, and added it as a little flirty statement (what she says beforehand leads to that too: "That was SOME dance party, Aang").

Most of all, though, I don't think she was ready to kiss him on the lips. I believe she does have feelings for Aang that are still beneath the surface, but she can't express those feelings if she hasn't realized they exist yet. The flirty kisses on the cheek, I think, were caused by tiny little moments in which the hidden feelings bubbled up to the surface. They just weren't noticeable enough for her to really think about it. Katara sees all these little bits of Kataang she occasionally shows as specific to each situation--a flirty comment here, a kiss on the cheek there. She doesn't see all of these things as a whole like we shippers do; they're just separate moments that don't add up. In the DoBs kiss, however, I think all these little moments and realizations came rushing back to her at the same time, thinking back on her and Aang's history through all the shock. The only time she consciously thought about it before was in "The Fortuneteller":

Sokka (watching Aang): Man, sometimes I forget what a powerful bender that kid is.
Katara (her expression changing): Wait...what did you just say?
Sokka: Nothing, just that Aang's one powerful bender.
(Katara stares at Aang for a moment before responding.)
Katara (lost in thought): I suppose he is.

I bow down to your powers!

we can take my friend's comment ( 3. maybe a little disgusted/dissapointed with herself?) 3 ways

1- she didn't like that Aang kissed her, it felt wrong. But that would mean she would not have been comfortable talking to him afterwards in a normal way- very unlikely

2- She thought "why didn't I see this sooner, all the signs have been there; but now is when I see that he loves me"- and now she has to sort what are her feelings toward him. And go from there- this is most likely

3- she thought "why is he in love with me? There are many girls who would be better for him than me. I don't deserve to be with the Avatar"- unlikely