She may also try to find a way to turn the situation around without giving in to the blackmailer's demands. Hermione is resourceful, so she might seek help from her friends in a very discreet way. She could use magic in creative ways to protect herself and the secret that the blackmailer is using against her. For instance, she could use a spell to make the evidence the blackmailer has useless.
In many fanfictions, Hermione's reaction is also influenced by her loyalty to her friends and the wizarding world. If the blackmail involves something that could harm them, she would be even more determined to fight back. She might sacrifice her own reputation or safety to protect those she cares about. For example, if the blackmailer threatens to expose a secret that would get Harry expelled, Hermione would go to great lengths to stop that from happening.
Hermione usually reacts with a mix of anger and determination. She's not the type to be easily pushed around. So, she might start by trying to figure out who the blackmailer is and what their motives are. For example, she could use her intelligence to set traps or follow leads to expose the blackmailer.
She might initially be shocked and scared. But then she would start to think rationally and try to find a way to outwit Snape. For example, she could start to gather evidence against Snape's own wrongdoings, if there are any, so that she can turn the tables on him.
In 'Hermione's Ordeal', she is initially shocked but quickly composes herself. She tries to negotiate with her kidnappers, using her wits to buy time. She also attempts to analyze their motives and weaknesses, which is very Hermione - like. She doesn't just sit there and wait to be rescued; she actively tries to find a way out of the situation.
She often tries to ignore it at first. She's focused on her studies and doesn't want to give the bullies the satisfaction of a reaction.
In most of these fanfictions, Hermione reacts with her characteristic intelligence. For example, in 'The Captive Hermione by Greyback', she immediately starts to analyze her surroundings and look for possible escape routes. She uses her knowledge of spells and potions to try and gain an advantage over Greyback.
One common plot twist could be that the blackmailer is someone she least suspects, like a fellow Hogwarts student who has a hidden agenda. For example, they might be jealous of her academic achievements and use some secret they've uncovered to try and undermine her. Another could be that the blackmail involves a dangerous magical secret she's been entrusted with, and if it gets out, it could put the wizarding world in jeopardy.
Often, Hermione reacts with a mix of shock and anger. She's a strong - willed character, so she doesn't just take it lying down. In some fanfictions, she immediately confronts the cheater and gives them a piece of her mind.
Hermione would probably be defiant at first. She's not one to take injustice lying down.
Hermione could become withdrawn. She might isolate herself from her friends for a while, spending her time in the library trying to make sense of it all. She might also feel a sense of betrayal, especially if they had some sort of understanding or relationship developing.
She might withdraw. Hermione could become quiet and start spending more time alone, like going to the library even more often than usual. This is her way of protecting herself from further hurt.
She might initially be in shock. Hermione is used to relying on her friends, so the betrayal would be a huge blow. She could then become angry and start to isolate herself. In some fanfictions, she might try to figure out why they did it on her own, using her intelligence to uncover the truth.