Woefully way behind again, since part 2 came out today...
In any case, if she told AS some crazy story about how Gannon was mad at her for something and left in a huff, then AS might believe her when she suggested they use a different car, so that Gannon wouldn't hide when/if he saw the truck. (Now watch this be in her next round of verbal diarrhea online somewhere).
Except... the police have known from the beginning, the description of the person who came and got him, and the person who sent
that person, and all of that.
Because, she took of selfie with her phone from Gannon's phone while they were parked on the side of the road in the driveway.
Because, gate key.
Makes sense to me.