A tip on writing fights scenes, if you are having troubling getting a scene across change the perspective. Have the POV change to Katara or Sokka dealing with Zuko while the big battle happens off screen and only the aftermath is seen.

Like a big smoking crater.

And I would be delighted to see girl!Sokka applying some scientific principles to waterbending. Why does this work and not this. Can Katara bend other liquids? what ratio to water does it have to be? Bloodbending couldn't be far behind. Learning to drop blood pressure is a good non violent way of getting bad guys out of the way without seriously damaging them.