In 'Hermione gets a Howler' fanfiction, it could be that the Howler contains some sort of secret or long - hidden truth. For example, it could reveal something about her family that she was unaware of. This would not only shock Hermione but also change the way she views herself and her place in the wizarding world. It could also create a rift between her and her friends if they react differently to this new information.
Well, in the fanfiction, Hermione might be publicly scolded by the Howler in front of her friends. This could lead to her feeling extremely embarrassed. Maybe she made a mistake in her studies or violated some school rules in the fan - created scenario.