She might be shocked at first. Since they are usually comrades or friends, Percy screaming at her is out of the ordinary, so she could just stand there in disbelief for a moment.
Another possibility is that she tries to calm Percy down. Annabeth is smart and level - headed. She might realize that there is something deeper going on with Percy and instead of getting into an argument, she attempts to soothe him and figure out what's wrong.
Annabeth could also get angry in return. She is a strong - willed character. If Percy screams at her without a good reason in the fanfiction, she might fire back with her own sharp words, not willing to take the unjust treatment.
She might be heartbroken at first. She could try to jog Percy's memory by showing him things that were important to them.
Annabeth could also be angry, not at Percy but at the situation or the forces that led to his death. She might vow revenge and start on a journey to find out who or what was responsible for Percy's sacrifice and make them pay. This could lead her into a whole new set of adventures and challenges as she tries to come to terms with her loss.
She's probably super excited. She might run and give him a big hug right away.
He could also become withdrawn and depressed. Percy and Annabeth have a very strong bond, and her death would leave a huge void in his life. He might isolate himself from his friends and family, lost in his grief and memories of her.
Annabeth could be annoyed. If she doesn't understand why Percy is staring, she might think he's being rude or wasting time. So she could give him a sharp look or a sarcastic comment to snap him out of it.
She might be initially very angry. Annabeth is intelligent and perceptive, so she would likely feel betrayed that Percy thought he could deceive her. For example, if Percy lies about a mission, she could find out the truth later and confront him immediately, demanding an explanation.
Annabeth's reaction could vary. If she's been missing Percy a great deal, she'll be overjoyed. She might show him around the school, proud to introduce him to her friends or teachers (if possible in the context of the fanfiction). However, if she's in the middle of something important like a test or a big project, she could be a bit annoyed at first but still be happy to see him deep down.
She could also become cold and distant. Instead of engaging in a shouting match, she might simply walk away and give Percy the silent treatment. This can be a powerful reaction as it makes Percy realize that his yelling has pushed her away and he has to make an effort to fix things.
Then, she would probably be angry. Annabeth is a strong - willed character. She would feel betrayed and used, and her anger would fuel her to find out the truth. She might start her own investigation to figure out what's really going on with Percy, whether he's been influenced by someone or if there's another reason for his actions.
Well, in many such fanfictions, Percy might be extremely flustered. He could blush furiously and quickly look away, being the gentleman that he is. After all, he has deep respect for Annabeth.