One possible reason could be that she is in a desperate situation. Maybe she needs something for a very important spell or potion to save someone's life and she thinks Harry won't notice or will forgive her. For example, if there is a rare ingredient that only Harry has access to and time is running out.
Perhaps she is being influenced by some dark magic or a cursed object. This could cloud her judgment and make her do things she wouldn't normally do, like stealing from her friend. It might be that the object she steals has some sort of power over her that she can't resist.
Another reason could be a misunderstanding. Maybe she believes that something Harry has actually belongs to her or was wrongly taken from her in the first place. So in her mind, she's not really stealing but reclaiming what is rightfully hers.
One possible motive could be that Hermione believes the grimoire contains powerful magic that she thinks is necessary to defeat a great evil. She might think Harry is not using it to its full potential or is unaware of its true importance.
Maybe she's desperate for some knowledge that she thinks Harry has in those books. For example, if the books are related to some dark magic or ancient spells that she wants to study for the greater good, she might be tempted to take them without asking.
One possible reason could be that Hermione wants to pursue her own independent magical research. She is highly intelligent and may feel the need to focus on her studies without the distractions that come with being close to Harry. Another reason might be a disagreement over some major decision in the wizarding world. For example, if Harry has a different stance on how to deal with the remaining Death Eaters or how to reform Hogwarts' curriculum, Hermione, with her strong opinions, may choose to distance herself to avoid constant conflict.
If Hermione realizes her mistake and tries to make amends, it could lead to a deeper understanding between them. They might have to work through their feelings and have some difficult conversations. For instance, Hermione might have to explain her reasons fully, and Harry would have to decide if he can forgive her.
Yes, there are some out there. Some fanfictions explore this alternative relationship dynamic in interesting ways. They might rewrite the story's events and character interactions to make it seem more plausible for Harry to be with Hermione instead of Ron.
At first, Harry would be angry and confused. But as the story progresses, if Hermione has a valid reason for stealing the grimoire, they could start to repair their relationship. However, there would always be a shadow of doubt and a sense of unease between them. For example, Harry might be hesitant to share important things with Hermione in the future.
It could also be due to a series of unlucky events. Suppose Hermione's well - intentioned plans keep backfiring in a way that makes Harry question her judgment. Like when she tries to solve a problem but ends up making it worse, Harry might start to lose trust.
Another reason could be that there are some misunderstandings between them. For example, Hermione might misinterpret Harry's actions or words as being too reckless or irresponsible, and she decides to push him away to avoid being dragged into what she perceives as a bad situation. Also, it could be related to her own insecurities. She might feel that she is holding Harry back in some way or that their friendship is becoming too complicated, so she takes the step of pushing him away to simplify things.
The plot could start with Harry realizing he has deeper feelings for Hermione than just friendship. He might start spending more time with her, which causes tension between him and Ron. Eventually, he could confess his feelings to Hermione, and she might be conflicted because of her relationship with Ron.
One reason could be that the troll is simply on a rampage and Hermione was in the wrong place at the wrong time. Trolls are not known for their intelligence, and it might have just stumbled upon Hermione while wandering the Hogwarts halls.