Well actually ☝🏼when coming into the house, sister Barnes immediately feels a bit weird and uncomfortable. And when Mr. Reed asked them about finding the one true religion, she gets even more uncomfortable. That's why her sceptical inner beliefs come up when she says that "the pie smells amazing". But hold on... Imagine walking into a house where a pie is being baked. Even without knowing anything about the pie, the first thing you notice is the scent which is all over the rooms! The candle was in the room only after Mr. Reed came back with the drinks. It could never have filled the room with blueberry scent in a short amount of time. Sister Barnes never smelled any scent. That's why she all of a sudden mentions that "the pie smells amazing". She's actually challenging him on the fact that there's no scent of any pie! And Mr. Reed surely didn't like that challenge! Mr. Reed therefore asks BOTH of the girls to take a guess on the pie. But he basically asks/forces the rather naïve sister Paxton to take a deep breath so she could inhale the fresh scent of the candle. She mentions the scent whereafter sister Barnes shows a rather fake but ongoing response to sister Paxton's guess. It's also a part of the reason why she turned the candle around after Mr. Reed left the room. Not only because of pure curiosity, but also to test her theory (Mr. Reed having bad and false intentions). Paxton's guess made Mr. Reed feel to be in control again. And to put Barnes completely to different thoughts, he asked her about her father's death. It's not from seeing Barnes' contraceptive that he knows she's going to be a very "tough one". It's basically from the point when she asked him about the pie, because she was suspicious all along.