It could be that she enters a magically - enchanted room where there is a strange mist or fog. As soon as she steps in, the mist clings to her and makes her wet. She didn't expect this as she was exploring the room thinking it was just a normal part of the castle. This situation might put her in danger as the wetness could affect her ability to use magic properly, like if her wand gets slippery.
One possible plot could be that she's caught in a sudden rainstorm during a crucial moment, like when she's on a mission to find a hidden magical object. The rain soaks her, and she's frustrated because it might ruin the parchment with the clues she has. And she can't use a spell to dry off immediately as it might draw unwanted attention from dark forces in the area.
An old - fashioned pure - blood wizard who doesn't like Hermione's Muggle - born status. He sees her as an outsider and wants to make her life difficult at Hogwarts. He uses a charm that causes water to seep through her clothes whenever she enters certain areas of the castle. This is his way of trying to drive her out of Hogwarts.
One possible plot is that Hermione, as a boy, decides to join the Quidditch team. Since she has always been a studious person, she now has to balance her academic pursuits with her newfound athletic ambitions. She might face some discrimination from the other male players at first, but eventually wins them over with her skills and strategic thinking.
Some dark wizards or witches who oppose the new order at Hogwarts after the fall of Voldemort could also be the villains. They might see Hermione as a threat to their plans of taking over or causing chaos in the wizarding world. They could force her to do things against her will in order to gain an advantage over the good side.
Well, it could be about Hermione getting caught in the rain while at Grimmauld Place and then having to deal with being soaked. Maybe she has to quickly find a way to dry off and in the process, there are some interesting interactions with the other characters who are also at Grimmauld Place.
Well, perhaps the plot could involve Hermione being bitten by a vampire during one of her adventures. Then she has to deal with her newfound vampiric nature while still trying to maintain her relationships with Harry and Ron. She might struggle with her thirst for blood and her moral code as a witch.
It could be about Hermione having an accidental or magical encounter while near a broom. Maybe she's in a rush and brushes against it in a way that sets off a series of strange events, like the broom starts to glow or move on its own.
One possible plot could be that they are in a dangerous situation together. Maybe they are facing a dark wizard attack and have to take cover against the wall. They could be using their combined magical skills to fend off the attacker. For example, Hermione might be using her quick - thinking and vast knowledge of spells, while Bill with his experience as a curse - breaker could be using his more practical combat magic.
Maybe there was a potion spill. A cauldron could have tipped over, and the liquid inside splashed onto Hermione, making her wet.
One possible plot twist could be Hermione getting tired of being overlooked in the wizarding world despite her intelligence. She might turn to the Dark Arts out of a sense of vengeance. For example, she could start using her knowledge of spells to manipulate those who have underestimated her, like some of the pure - blood supremacists. Maybe she'd form her own group of followers who are also disillusioned with the current state of the wizarding world order.
It's hard to say for sure as it's a very strange and specific concept. Maybe it could be some sort of magical accident where Hermione is affected by a charm on the broom and has an unusual interaction. But this is just speculation.