I'm not sure specifically as there could be many different interpretations in fanfiction. It might be about a situation where The Order, perhaps in the Harry Potter universe, betrays Hermione in some way, like leaving her in a dangerous situation, or not believing her when she has crucial information.
In fanfiction scenarios where Hermione is betrayed by the Order, it could be related to a prophecy. Maybe there is a prophecy that involves Hermione in a way that the Order misinterprets. They think that by betraying her, they are saving the wizarding world. Or perhaps there is a conflict of ideology. Hermione might have some new ideas or approaches to magic that the more traditional members of the Order oppose. And they see her as a danger to their established ways. Also, personal grudges among the Order members could spill over. If someone in the Order has a long - standing grudge against Hermione for some past incident, they could convince others to betray her.
Obviously Hermione is one of the main characters. As for the others, it could include members of The Order such as Dumbledore, Sirius Black if he was still alive in the context of the story, and other Order members who are involved in the act of betrayal.
It could be that a member of the Order, out of jealousy or a wrong perception of Hermione's power, convinces the others that she is a liability. So, they betray her by not believing in her when she discovers something important or by preventing her from using her skills to help. Hermione, being the strong - willed character she is, would then strive to prove them wrong and expose the real issues within the Order.
She would probably be very hurt and angry. Hermione is a strong - willed character, so she might immediately start trying to find out the truth and clear her name.
It could be a new character introduced in the fanfiction. Maybe someone who has infiltrated the Order and wants to create chaos by turning them against Hermione. This person could be a spy from the Death Eaters or another dark - aligned group, with the goal of weakening the Order from within by making them lose one of their most intelligent and powerful members.
It depends on the specific plot of the fanfiction. It could be a friend who turns against her due to jealousy, or perhaps a false ally within the so - called 'light' side who has ulterior motives.
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.
Yes, there are some out there. One example might be on FanFiction.net. You can search for it using those keywords and look through the reviews to find a well - written one. However, different people have different ideas of what 'betrayal' means in this context, so you might need to read a few to find the one that suits your idea.