back on topic
pretending that Katara will definitely decide not to have a "romantic ship" with Aang
there are a few things even a hardcore Zutarian(ones who think that Zutara will happen, no chance for Kataang) should have as a given
Katara has a very deep friendship toward Aang(think Will and Grace)
she thinks highly of Aang
if she didn't know before, she NOW KNOWS Aang loves her
she felt comfortable with him at the end of DOBS
she was surprised about the kiss, at first she was tensed, but than she relaxed
she continued in "the act of kissing" even after Aang pulled out
in comic styling "colored cheeks always means Embarrassment, only exceptions is sickness or a permanent colored cheek(like Howdy Doody); Katara was not sick, and is not a permanent part of her, thus she was embarrassed
now Pretending that she has or will decide not to pursue a romantic ship with Aang
we have all to agree that Katara decided to correspond his kiss, than if we pretend she doesn't plan to have a romance with Aang, the only thing we might draw that definitely favors she doesn't have romantic feelings is this, that she felt bad(thus embarrassed) that she might have lead Aang to conclude that she wants something romantic with him; if that was the case she would not have been highly comfortable with him at DOBS.
conclusion
if we pretend that she has or will decide not to have a romance ship with Aang, she felt embarrassed that she has to decide her feelings for him or see him in a different light; since we are pretending she will decide not to pursue it, than she must have put that decision for later, and concentrate on things on hand, and that is why she felt comfortable with Aang at the end of DOBS.(she acted as the caring friend, without worrying about how things are between them) and the earliest she has made a decision about Aang being just a friend and nothing more is after WAT, not before, and she can easily still be pondering it at the start of 314(this is if we pretend she will decide not to have a romance with Aang)
if we pretend she will be with Aang at the end, she might already decided to be with him at the final part of DOBS
if Zutara happens, Zuko not only has to gain her love, he has to make her feel sure that there is nothing for her and Aang in the romantic sense and to close all doors between him and Mai.