A mother must do whatever it takes to protect her child.
She hugs Zuko, wiping the tears from his cheeks as she tells him not to be afraid. "Never forget who you are," she whispers as she releases him, slowly walking away. She tries to blink away the image of the boy's scared, confused face as she closes the door behind her.
When she comes to Azula's room, Ursa takes a deep breath and knocks. When she recieves no answer she pushes the door open and slips inside.
"Azula," she whispers, leaning over the girl's sleeping form, "honey, I need to go away...I don't know when or if I'll ever come back."
Azula only snores; she's either sleeping too deeply or pretending she is. Ursa sighs, kneeling beside the bed and stroking her daughter's cheek.
"I love you, Azula. No matter how often I've scolded you I love you so much, don't ever forget that," she says, tears brimming in her eyes as she kisses the girl's forehead. Azula stirs slightly, murmuring softly as she presses her face deeper into the pillow. I'm sorry, Azula, I'm sorry that to protect your brother I must hurt you both by leaving you behind.
As she leaves, Ursa whispers a silent prayer to the Spirits. For Zuko, the strength and courage he needs to be himself. For Azula, guidance towards the right path and to make sure her gift never goes to waste. And for Ozai, to remind him that he is loved, and not a day wil go by that she doesn't think of him.
Six years later, the memory surfaces as a hallucination in a mirror. I love you, Azula, I do. When the glass shatters and her mother's image disappears, Azula buries her face in her arms and cries.