She could also be shocked and a bit scared at first. But then, using her intelligence, she might try to figure out why Snape did such a thing. Maybe she would start analyzing the situation, thinking if there's some hidden danger or if Snape has lost his mind, and then act accordingly to protect herself and others.
Hermione might retaliate magically. Given her proficiency in magic, she could use a simple spell to make Snape let go of her hair. And then she would likely report this incident to Dumbledore or other authority figures in Hogwarts, as she believes in following the rules and would not tolerate such inappropriate behavior from a teacher.
She would probably be very angry. Hermione is a strong - willed character. She might immediately try to break free from his grip and demand an explanation. For instance, she could shout at him, 'Professor Snape, what do you think you're doing? This is completely unacceptable!'
One possible reason could be to get her attention in a very forceful way. Snape is often a complex character in fanfiction, and he might be trying to make Hermione listen to him urgently, perhaps about a dangerous situation in Hogwarts that she's not aware of.
She might decline. Hermione is a very practical and goal - oriented person. She has her studies and her friends to think about. Going on a date with Snape, who has a rather complex and not - always - friendly reputation, might seem too risky and not in line with her plans. Also, she may not have any romantic feelings for him at all.
Hermione would probably be very confused at first. Snape has always been a rather intimidating and strict teacher, so his sudden change in behavior would be quite a shock. She might initially think it's some sort of trick or test.
Hermione might initially be very suspicious. Given her intelligence and wariness, she would not easily fall for the temptation. She would likely question Snape's motives and try to analyze the situation from all angles.
She would probably be defiant. Hermione is a strong - willed character. She values her independence and her ability to make her own decisions. So, she would likely question Dumbledore's motives and resist his control. For example, she might start her own investigations secretly to find out why Dumbledore is acting this way.
She might say yes right away. Hermione has deep feelings for Harry as a friend, and those could easily turn into romantic feelings. She would see all the good in Harry and believe that they could have a great relationship together.
Hermione could also be very hurt. Her hair is part of her identity, and having Draco, who she already has a strained relationship with, do something so cruel would cut deep. She might go to her friends, Harry and Ron, for support. They would likely be just as angry as she is and plot some sort of revenge against Draco and his Slytherin friends.
She might give him cold stares in class. Hermione is not one to shy away from showing her emotions through her expressions. So, every time Snape is in her line of sight, she could fix him with a withering glare that clearly shows her displeasure.
Snape's brooding and mysterious personality might work in Hermione's favor. His intimidating presence alone could deter some of her enemies. People in the wizarding world might be afraid to cross him, so they would think twice before harming Hermione if they knew Snape was protecting her.
Her character could develop through her relationships. She might befriend students from all houses, which is a bit unusual in Hogwarts. This would be because she has qualities from both Gryffindor (from Hermione) and Slytherin (from Snape). Through these friendships, she'd learn different perspectives and grow as a person. For instance, she could teach her Gryffindor friends about the subtleties of Slytherin thinking and vice versa.