Lord Zuko nods. Reluctant though he is to discuss it, especially now of all times, if she's already read about it there's no point in hiding the truth from her. Better for her to hear the whole story now, than to get by on headline-grabbing half-truths. "Yes. You know already that the Red Lotus's goal was to eradicate the Avatar, and the Avatar Cycle itself, for good. They very nearly succeeded, had the airbenders and Suyin not come to your aid."

There's a moment's pause as he lets the implications of that sink in. Then he lifts his gaze to look her in the eye. He had promised he would be her confidant if she needed him, and that means not hiding the truth from her, no matter how painful. He would do no less, if it had been Aang in the same position... So, expression darkening, he continues.

"Zaheer poisoned you. His idea was that it would force your body into the Avatar state, and from there... end it. Although you survived, you were left severely weakened from the ordeal."