Book 2 is worse, all the lessons she learns in book 1—like leaning on Tenzin's wisdom instead of fighting him, being less hot headed, accepting responsibility for her own actions—is out the door.
She betrays her dad because her uncle accused him of a crime from 30 years ago, that she could have no way of verifying. The Evil Avatar plotline is underbaked and resolved in 1 book, which IMO sets it up for disaster. You need to work on that, you can't set up an evil counterpart to the focal figure in the show and then wash your hands of them in the span of 5 episodes.