I actually think that both Mary and Henry told Emma about their conversations with Graham. Didn’t Emma say that he was running around talking to people and she was waiting outside the door to Henry’s house which suggested to me that Mary called Emma after Graham left her classroom. I am not saying that is enough to believe. I think her biggest reason is that August is sane. He isn’t crazy. And he seems sincere. The thing is she thinks he is lying because he is a liar, but he has no reason to lie.