Why is Annabeth needed on the new mission?

Chiron tells them that it was the Roman camp who defeated the Titan base on Mount Othrys during the Titan War. They know that the Roman camp is somewhere near San Francisco, but they have no exact location. Jason plans to try to find it and sail there in Leo's flying ship to persuade them to join forces. He tells Annabeth she will be needed on this mission as her boyfriend Percy Jackson has been sent to the Roman camp as an exchange, and, like Jason, probably does not even know who he is.