Annabeth has been forced to look after herself and act older than she is her whole life, except for the 6 months she was with Luke and Thalia. Although that wasn't necessarily safer than the rest of her life, she had someone else looking out for her, treating her like a kid, because she was genuinely still so young when they found her. And now she has to consider the possibility that the short time she spent as just a kid might be the thing that destroys her judgment. Maybe she's wrong about everything because she had someone there to shield her.
And then the person she used to love and trust more than anyone in the whole world tells her she doesn't understand anything and that she was too young to see things how they were, and that's devastating to her. When someone you love and used to trust tells you something in such a harsh way, you have a hard time brushing that off.
They're still so young and there's so much that they don't know, but now she's going to be second guessing everything about the safest happiest time of her life.
