Weird idea I came up with:
When Draco is born, she’s a girl and the third Malfoy baby.
However, she’s the first baby to survive past ten minutes.
Narcissa is terrified of Lucius’ reaction if he learns it’s a girl and not a suitable heir.
She can’t handle another pregnancy, and fears for her daughter’s life, so she disguises Draco as a boy with a complicated spell.
Draco is raised as a boy, thinks he’s a boy, and doesn’t learn of the spell until after the war.
A few years after the war, Draco confides to Narcissa about questioning his gender. He explains “transgender” and asks her what she thinks.
Narcissa tells Draco the truth; he was born a girl but disguised out of her fear. With Lucius in prison and the Malfoy name dishonored, there’s no fear left, and Draco has a choice.
He’s angry at first, but forgives her and chooses to undo the spell. He doesn’t want to live a lie.
They undo it together, and Draco awakens in a female body. His mind hasn’t changed, nor his age, and he’s not 100% positive about his gender, so he goes with it.
Narcissa teaches him about the puberty he didn’t learn and shows him how to handle his new body.
It’s confusing, but he learns.
A few weeks after the transformation, Draco figures out she’s a girl. She tells her mother and fully transitions, using she/her pronouns and changing her name to Juno.
Her friends Pansy, Blaise, Greg, and Luna are very accepting and support her through the spell and transitioning.
Juno walks back into the Wizarding World with a new name and face. She takes the Black family name and uses the opportunity to restart her life.
After some studying, she gets a job at the Ministry and starts working. No one realizes her past, and she doesn’t tell anyone.
Her intelligence quickly propels her into higher positions of politics and academia.
Juno remembers the Black family tree, and visits Potter to see it. She explains that she’s a distant family member and wanted to check something, but doesn’t reveal her past.
Harry is confused, but allows it.
Juno finds that her name hasn’t changed on the tree. She’s disappointed and upset, but is consoled by her friends.
Then, Juno is assigned to work with Hermione Granger.
She’s terrified if Granger will recognize her, but she doesn’t. Then—despite Juno’s hesitance—they become good friends.
Juno ends up “meeting” Harry and Ron. She never reveals her past, and avoids the men when she can, but they do get to know each other.
Hermione doesn’t realize Juno’s past, either. Juno is scared that if she is honest, she will lose her friend.
Then, while Harry is fixing up Grimmauld Place, he decides to play around with the tapestry.
He and Hermione redo the spell so that the tapestry is no longer controlled by a single person’s magic. It adapts and changes to what the people subconsciously want.
Several names disappear, no longer wanting to be a part of the Black family, while several more appear, having become family members through bonds, not blood.
And a few of the names change, including Draco Malfoy’s.
Harry is baffled by the change, and when he points it out to Hermione and Ron, she recognizes Juno Black’s name.
Hermione confronts her friend and shows her the tapestry, who promptly breaks down and apologizes for lying. Hermione realizes what has happened and—remembering Juno’s kindness and attitude—forgives her.
Hermione explains what happened to Harry and Ron, who are shocked.
Then, Juno sees Harry and Ron again, and it’s quite awkward, but Hermione points out Juno’s change in attitude since the war, and the trio decide to get to know her more.
This could become anything now, so enjoy.