User blog comment:KrspaceT/The Seventh Demigod; Something unexpected?/@comment-110.32.249.166-20110713233334/@comment-4315730-20110819153930

It isn't set in stone that Annabeth will be the seventh in the prophecy. She wanted to go on the Argo II so she could go to the Roman camp and find Percy, not because she wants to go save the world in Greece. Jason agreed because if they find Percy, it would make sense to have Annabeth with them.