An alternate end for Azula and some exploration of a random idea I had: What if lightning bending had the potential to harm its user as well as its target? And Azula does love her lightning...
Lightning was the most powerful element you could bend, the most deadly, her father said. Done just so it could kill your opponent in one clean shot. The day Azula's talent reached this peak, she couldn't have been happier.
She never considered the double meaning her father's words had until it was too late.
It started shortly after the invasion, when she suddenly fell short of breath. Her heart felt as though it was literally pounding in her ears, her head was spinning. I'm just tired after the battle, she told herself. It wouldn't happen again.
During the battle at Boiling Rock, Ty Lee said she was looking a little sweaty and tired. Azula brushed off the girl's concerns. I'm not so weak. But as time went on, even she couldn't deny something might really be wrong. She used to feel energized after practicing her lightning bending, but now all she felt was drained.
When she suddenly collapsed in her chambers a few days before the comet arrived, the family physician gave her the news she'd been silently dreading. "Extensive use of lightning bending has weakened your heart, Princess. If you continue at the rate you've been, you will not live long."
"That's impossible," she snapped.
"I'm afraid not. In fact, the next time you attempt to bend lightning could be your last! I highly recommend you stay in bed for week, get plenty of rest, and don't practice bending of any kind for six months."
With his words in mind, she decided her death would be on her own terms. When Zuko arrived a few days later to challenge her for the throne, she didn't hold back. Her final lightning strike didn't even reach its intended target, sparking a few inches away from her feet before her heart finally gave out and she collapsed.
The last thing she saw was Zuko's saddened eyes looking into hers before everything faded.