In Chapter 37, who figures out where Virgil is and how does she do it?

In Chapter 37, Valencia figures out where Virgil is by piecing together all the things she has seen and heard all day long - Chet's claim that he was in the woods all day, Gen's revelation that Virgil was asked to collect stones for Kaori, and Chet's claim that he killed the snake and threw it down the old well.