Disclaimer: I don't own Avatar: the Last Airbender.
Vengeance
His perfect little tool had lied to him. She had protected herself from his wrath by hiding behind her weak brother. As it sent ice through his veins he wondered for a few moments if that was what it was like to be a waterbender and he cursed Azula for leading him to such an inferior thought. She'd pay, she would pay dearly, more so than defiant brother.
She walked and talked around him unaware of the accumulating hate building from her lies surrounding the Avatar's death. Ozai was enrage with the evidence that she perceived herself safe although she hadn't known Zuko had outed her. He reasoned she should have known something wasn't right by the way he was behaving toward her and how he had treated her the last few weeks.
He couldn't act now while she was still useful and needed, but his thoughts were consumed by various ways he'd extract his revenge for ever thinking she was worthy to be relied upon. He'd make her regret! She would think Zuko was fortunate to be awarded a scar with what she would suffer.
It would have to wait, but he could be patient this time, although he was still very eager. He was willing to wait to be able to savour the experience.
Sozin's comet was just a few days away and he hoped to upset her with the news she wouldn't be coming with him to raze Ba Sing Se to the ground. He had concluded that she would only be an added distraction, something to fuel unwanted anger when he desired a clear head. He decided to leave her home, a fitting start to her punishment. She wouldn't get to fulfil her plan and he chuckled at the thought knowing exactly how she would feel.
He realised he had been far too lenient with her because of the pride and joy she had once brought him. But now that she had betrayed his trust by lying. It was obvious she no longer feared him, once he returned and the war was over, he'd be sure she knew of that mistake.
Ozai smiled cruelly, he could already imagine her screams.
Author's Note: I have no idea how Ozai would punish her nor would I like to think about it. I decided to leave it up to your imagination, but I'm pretty sure it wouldn't be kind words and lollipops, unfortunately. If you would like to share your thoughts on the matter, please feel free to leave a review or not, it's entirely up to you.