She wasn't being a 'brat' she lost her mind. You think Zuko was the only one badly affected by the family drama? She had nobody but Ozai- who corrupted her into being a weapon. She had no love. She's also only 14.
Zuko had her committed to a mental institution, and in the recent graphic novels "the Promise" and now "the search-part 1" Zuko saw to it that she was well cared for. In fact, in "the Search part 1, Zuko has her released from the institution to join him in searching for THEIR mother. Unfortunately we see her still behaving "badly" and having delusional conversations with Ursa.
