One reason could be that Rachel represents a different world to Percy. She's more of an outsider to the demigod world, and Percy might be attracted to that sense of newness and freedom she seems to offer. Maybe he's tired of the constant danger and drama in the demigod life with Annabeth.
Well, it could be simply due to a different kind of chemistry. Sometimes in fanfiction, the author wants to explore an alternative relationship dynamic. Reyna has a certain allure and mystery about her that might attract Percy. And the story could be set up in such a way that Percy and Reyna have more shared experiences at a particular point in time, which makes him lean towards her instead of Annabeth.
She could be heartbroken. Annabeth has been through a lot with Percy, and to be rejected for Rachel might make her feel like all their adventures together meant nothing.
Well, it could be about different understandings of Percy. Annabeth knows Percy as a demigod, as a hero in their world. Rachel, on the other hand, might see Percy in a different light, more as an individual outside of the demigod stuff. They might fight because they both think they know what's best for Percy and how he should be. Also, it could be a fight for Percy's future. Annabeth might want Percy to stay in the demigod world and continue their adventures together, while Rachel could have different plans for him.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
Perhaps Annabeth made a decision without consulting Percy that put him in danger. In the fanfiction world, this could lead to her feeling guilty and apologizing. For example, if she led their group into a trap because of her over - confidence, she'd realize her mistake and say sorry to Percy.
Maybe he was hit by some magic or a spell that affected his memory. It could also be due to some sort of trauma he experienced that made his mind block out his memories of Annabeth.
One possible reason could be a misunderstanding. Maybe she saw Percy doing something that she misinterpreted as a betrayal of their friendship or their cause. For example, if Percy was seen talking secretly with an enemy, Annabeth might jump to conclusions without knowing the full story.
One reason could be Jacob's more down - to - earth nature. He represents a more normal, warm - hearted life compared to Edward's rather cold and sometimes brooding vampire existence. Bella might be drawn to the simplicity and closeness to nature that Jacob offers.
Maybe she's scared because the fanfiction portrays Percy in a way that's out of character for him. Like, it might show him being overly aggressive or having strange powers that she doesn't recognize, which makes her feel like she doesn't really know him anymore.