There could be an older student who is kind and has a sense of justice. This student might see what's happening to Annabeth and decide to help. They could use their influence among the students to put an end to the bullying. Maybe this older student has been through something similar before and doesn't want Annabeth to suffer the same way.
Her family could be a great help. If they are aware of the situation, they can step in. Maybe her parents can talk to the school authorities or even directly to the bullies' parents. Family support is always crucial in such situations.
Well, she might consider making some new friends who are strong and kind. In the 'annabeth gets bullied at school fanfiction', if she has a group of friends by her side, the bullies might be less likely to target her. Friends can also give her support and make her feel better. For example, they can stand up for her when the bullies are around or just be there to listen when she's feeling down about the bullying.
Maybe an antagonist who wants to disrupt the group dynamic. If Annabeth is a key part of a group, punching her could cause chaos and confusion among her friends. It could also be someone who has been influenced by dark magic or some sort of mind - control in the fanfiction. This would make them act against their normal nature and punch Annabeth without really having a personal grudge.
Maybe it's a human who has somehow discovered the world of demigods and is afraid of their existence. They shoot Annabeth out of fear and misunderstanding. Another option is that it's a rogue demigod who has gone bad and is working against their own kind. This character could have a personal grudge against Annabeth specifically, perhaps because of her intelligence and leadership skills which they envy.
It could be an enemy from the underworld. Maybe a powerful demon or a vengeful spirit that has a grudge against her. They might use their dark powers to harm her, like sending a bolt of dark energy her way.
There's a chance it could be a new character introduced in the fanfiction. Maybe someone who has a mysterious past and enters Annabeth's life briefly but leaves a big impact, resulting in her pregnancy.
Percy would probably be an important character. He's Annabeth's close friend and love interest. His reaction to Annabeth getting her period could be interesting, like he tries to be supportive but is a bit clumsy at first.
Her close friends would most likely be involved. Percy, for sure. He would probably be worried about her and try to sober her up. Grover might also be there, trying to use his nature - related powers to find some herbs or something that could help her feel better.
Percy might initially be confused. He would probably wonder why Annabeth, who was once his friend or ally, is treating him this way. So he could try to talk to her to find out what's wrong.
Percy might be one. They have a close relationship, and in some fanfictions, he could be more forward with his feelings through flirting.
It could be new girls who come into the camp. They see Annabeth's position and all she has achieved, like her close friendship with Percy and her role as a leader, and they become jealous. Maybe some minor characters who have always been in the background and feel overshadowed by Annabeth.