Author's Note: Disclaimer that I don't own Harry Potter or anything else affiliated with it, that would be JKR's purview.
Also, for the purposes of this story, I imagine Luna using ASL, as it is all that I'm familiar with.
She lives in a world of silence and meaningless sounds.
The tangle of lips and tongues and teeth across from her are a mystery that she doesn't want to solve. The Healers try to demand otherwise, but Luna doesn't care. She has her writing, straggling across the page, and she has her signs. Her signs are more important than reading someone's lips, twisting and writhing like thin worms.
Her father doesn't try to demand she lip read. He learns to sign instead, his hands clumsily following her cues. Luna is patient, like her mother was before the accident, and if sometimes her eyes are wet after, she can blame it on the Nargles.
When she goes to Hogwarts, her teachers don't understand, but they are kind. She is Sorted into Ravenclaw, and Flitwick gives her the bed next to the door.
Her classmates do understand, and they are cruel. It takes no lip reading to understand the cruelty that twists their faces, their disgust for the blonde-haired, waif-thin first year with the bright purple hearing aids (that she is forever "accidentally" turning off) and the hands that move like swooping birds. She is different, and people don't like different.
It is halfway through the year before someone approaches her, proffering a note about her signs. How do you do that? Ginny Weasley asks with earnest brown eyes, haunted by ghosts Luna can't begin to understand. It is hard to teach her, with only her hands and hastily jotted notes, but she manages, teaching her how are you and my name is. Teaching her spell names in sign language and watching how sometimes, even without a flick of the wand that lies mostly forgotten in her pocket, they come true anyway.
Thank you, Ginny signs, her fingers awkward still, but the sentiment genuine, and Luna smiles, lopsided and gamine.
"You're welcome," she says aloud, her voice a bit too loud, her pronunciation a bit too open-mouthed. Ginny hugs her before she realises, and skips off, looking more lighthearted than she has all year. It is not until summer Luna finds out what has been riding the Weasley girl, and she wonders if You Know Who understands sign language now, but she doubts it. He could never see the power behind it, the freedom inherent in a few fluid movements.
When Luna comes back the next year, Ginny appears in her train compartment, and she's not the only one.
Can you teach us? Ginny asks, her looping handwriting scrawled across the page, and Luna smiles.
Yes, she signs back, radish earrings bobbing.