I don’t have a fic where Azula is much older than canon, but I do have one where Zuko is much younger, and that is close enough to be getting on with. Continued from: [Link]. I’m tackling the last option.
1. Azulon orders his granddaughter’s death, not knowing, or probably caring, that she is listening, hidden behind a curtain. Azula listens to her grandfather tell her father to kill her, and to her father replying that he will see it done by morning. Azula does the only thing she can. She runs. She’s in Lu Ten’s old room, fingers digging into the decerative wall paneling, because she knows there’s a secret passage behind it, Lu Ten showed her once when she was little, before he left, but she doesn’t know to open it, when her mother finds her. Whatever her mother had planned to say about disrespecting her dead cousin goes out the window as she looks at her, at her frightened tears and wild eyes. Kneeling down next to her, she puts her hands around her daughter’s face and asks, “What’s wrong?”
2. Azula never thought to tell her mother. If her father was going to kill her, why should she trust her mother? And what could her mother do against her father anyway? But confronted, when she’s so on edge, so trapped, it comes out. And her mother wipes away the tears, presses the hidden latch in the wall paneling, and gives her a tight smile. “I’ll talk to your father, and straighten this out,” she tells her. “You were smart to come here. If I’m not back in an hour, I want you to run as far and as fast as you can.” Then, she pushes Azula through the hidden door and shuts it behind her. Azula’s legs buckle. She sits in the darkness, arms wrapped tight around her knees, and waits.
3. But her mother does come back. She opens the door and tells Azula to come out. She leads her to her room, and tucks her into bed, and tells her that she has to go now, probably forever, but Azula will be safe. She tells her to please, please, please look after her baby brother, to teach him what he needs to know. Azula asks if she means teaching him how the hidden door works, and her mother says yes, exactly that. And Azula promises.
4. She never would have thought she would have been able to sleep that night, but eventually she does, her eyes drifting closed, her body refusing to stay awake any longer. When she wakes up, her mother is gone and her grandfather is dead. She finds her father in the courtyard near the pond, and summoning up all her courage, she asks where her mother went. Ozai doesn’t answer.
5. She goes to the nursery. She picks up the discarded Earth Kingdom doll, rubs the ash off her face, and tucks her in with Zuko. He grabs the doll and blinks at her, like he has no idea anything is wrong. As his nurse watches anxiously, Azula whispers promises to him, and swears she will take care of him and keep him safe.