The headmaster, Dumbledore, could also be the one to discipline Hermione. He has the overall authority in Hogwarts. If Hermione's actions endanger the safety of the school or other students in some way in the fanfiction world, Dumbledore could step in with a form of discipline, perhaps by restricting her access to certain areas of the school for a while.
One interesting disciplining Hermione fanfiction might be one where she is disciplined for breaking a school rule in a creative way. For example, she might be made to tutor younger students as a form of discipline for using magic outside of class without permission. This could lead to her growing as a character and learning more about patience.
When writing a disciplining Hermione fanfiction, think about the purpose of the discipline. Is it to teach her a lesson about humility? Or is it about following rules? Build the plot around this purpose. For instance, if it's about following rules, you can create a situation where Hermione breaks a new, important rule in Hogwarts. The discipline could be a series of tasks or challenges that not only punish her but also help her understand the importance of the rule. Make the language and dialogue in line with the characters' personalities. Hermione's dialogue should be intelligent and well - thought - out, even when she's being disciplined.
Another possibility is a jealous student at Hogwarts. There are always students who might be envious of Hermione's academic achievements. They could set up a prank or a trap that goes wrong and ends up hurting her. For example, a student who is tired of Hermione always getting the top grades in Potions might tamper with her cauldron during a class experiment, resulting in an explosion that hurts her.
Voldemort's remaining Death Eaters could be behind it. They might see Hermione as a threat to their attempts to regain power in the wizarding world.
There could be a group within the Ministry of Magic itself that is corrupt. They might not like Hermione's progressive ideas about the treatment of house - elves and other non - human magical creatures. So they conspire to put her in Azkaban to silence her and maintain the status quo.
Maybe a jealous wizard or witch within the Ministry of Magic. They might be envious of Hermione's popularity and influence among the younger wizards. So they fabricate evidence against her to get her locked up in Azkaban.
Well, it depends on how the disciplining is portrayed. If it's within the context of teaching a valuable lesson in a non - abusive way, it could be seen as appropriate in the realm of fanfiction. However, if it involves excessive force or goes against the general moral compass, then it's not.
Most likely, Harry and Ron would be the ones to take care of her. They are her closest friends, after all. They would feel a sense of duty to protect and care for her in this strange situation.
It could be Death Eaters. They are always on the hunt for Harry and his friends. If they manage to find Shell Cottage, they might see Hermione as a major threat and use a deadly spell on her.
One common theme is growth. The little brother usually grows as a person through the discipline of the older brother. For instance, he may become more responsible or learn important values.