She would be devastated. Hermione is a very emotional person deep down. She might isolate herself at first, not wanting to talk to anyone, even her closest friends like Harry and Ron. She'll probably go through a phase of denial, not believing that her parents are really gone.
She might also become more protective of her friends. After losing her parents, she realizes how precious life is. So she'll be on high alert for any threats to Harry and Ron. She could also start to question the safety of the Muggle - borns in the wizarding world and become an advocate for better protection for them.
They could have been put under some sort of spell by the Order to forget about Hermione. In that case, they would have just gone on with their lives, completely unaware that their daughter had been taken. However, if the spell was not perfect, they might have had some strange feelings or dreams about a missing child.
It could be that Voldemort's followers target Hermione's parents to get to her. They use a dark spell that slowly drains their life force. Hermione discovers this too late and has to face the guilt along with her sorrow. In the fanfiction, she could then seek revenge or focus on using her knowledge to prevent other wizarding families from suffering the same fate.
She would probably be in awe. After all, she has heard so much about them from Harry. She might be a bit nervous at first but would quickly warm up and start asking them all sorts of questions about their lives and magic.
Hermione's friends would likely be very excited. They might plan some special activities for her parents. For instance, they could arrange a little tour of the Forbidden Forest (from a safe distance, of course). They would also share stories about Hermione at Hogwarts, how smart she is and all the adventures they've had together. And they would be happy to answer any questions Hermione's parents had about the wizarding world.
Hermione could react by using her intelligence to expose Fleur's betrayal. She might start gathering evidence of what Fleur has done wrong and present it to their mutual friends or to an authority figure in the wizarding world.
Hermione might be shocked at first. She has always seen Draco as an adversary, so a neck kiss from him would be completely unexpected. She could push him away immediately and demand an explanation.
Harry would probably be very supportive. He knows what it's like to grow up without parents, and he would see Hermione's decision as a very kind and noble one. He might offer to help in any way he can, like teaching the child some of his own skills in magic or defense against the dark arts.
Hermione's parents in fanfiction can be portrayed in various ways. Some fanfiction authors might give them more magical abilities or knowledge than they actually have in the original story. This could be to create more interesting plotlines. For instance, they could have a long - lost relative who was a powerful wizard and this connection is explored in the fanfic, which in turn affects Hermione's journey in the magical world.
Hermione would probably be defiant at first. She's not one to take injustice lying down.
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.