There's also a chance that she could be slightly influenced in a positive way. If the fanfiction shows characters growing through kindness and understanding, although it's very unlikely for her, she might start to question her own extremely strict and cruel methods. But more likely, she'd just reject those ideas and double down on her existing behavior.
She could become even more vindictive. If she reads about characters who oppose her in the fanfiction, she might take it as a personal affront and start planning harsher punishments for any students who show signs of rebellion in the real Hogwarts, just like in the books.
She would likely be enraged. Umbridge has a very narrow view of the wizarding world and its values. Fanfiction can explore different relationships, alternate plotlines, and diverse interpretations of characters. This would go against her rigid beliefs. For example, if there was fanfiction that painted Dumbledore in a more negative light than she thought was appropriate, or if it showed Harry and his friends in a more rebellious and positive way than she would tolerate, she would be very angry.
She would probably be outraged. Umbridge is a strict and rather narrow - minded character in the original series. Fanfiction often takes creative liberties that she would likely see as subverting the 'proper' order of the wizarding world she thinks she upholds.
Harry's character would face a huge transformation. He'd be constantly on edge, having to deal with Umbridge's strict rules and her mean - spirited nature. This would make him more empathetic towards those who are oppressed. He'd also become more resourceful, finding ways to communicate with his old friends and allies despite Umbridge's attempts to isolate him. His experience with Umbridge would be a crucible that forges him into an even more resilient and determined hero, ready to take on not only Voldemort but also the corrupt elements within the wizarding establishment.
His confidence might grow. Military books are often full of tales of heroes and great leaders. Reading these could inspire Harry to be more assertive and believe more in his own abilities to lead and make tough decisions. For instance, he might be quicker to take charge in dangerous situations without hesitation.
She would probably be outraged. Umbridge is a strict and narrow - minded character in the original series. Fanfics often deviate from the 'proper' version of events she might think, and she'd likely see it as a distortion of the wizarding world she believes she upholds.
She would probably be outraged. Umbridge is a strict and conservative character in the original series. Fanfiction often contains ideas that deviate from the 'canon' she adheres to, and she might see it as a threat to the 'proper' understanding of the wizarding world she believes in.
The story would probably see a big change in the power dynamics at Hogwarts. Harry would use his power to protect the students from any more harm that Umbridge - like policies might cause.
She'd be appalled. Umbridge is all about following the rules and maintaining the status quo. Fanfiction doesn't adhere to the official canon she so firmly believes in.
She'd be disgusted. Umbridge is all about propriety and order. Fanfiction can be wild and creative, which is the opposite of what she stands for.
She might be enraged by how the characters in the fanfiction defy authority. Since she is a stickler for rules, seeing characters like Harry Potter getting away with things in the fictional stories could make her want to rewrite the fanfiction to suit her view of a proper magical world where students are always obedient and there are no challenges to the established order.