The Icy Gates

On a small group of islands, former fire nation colonies, people lived happily. That is until their king declined an arranged marriage between Princess Azula and his own daughter, (y/n). In response to this, the Fire Nation attacked ruthlessly, taking the islands' civilians captive.
Only their princess was able to escape, promising to return and free her people. But in order to do this, she's going to have to help team Avatar defeat the Fire Lord.