In answering your question, I think you are talking about the first Act when Betty first speaks among the girls. Betty accuses Abigail of drinking blood. Furthermore, she note that Abigail drank a charm to kill John Proctor and Goody Proctor. The word 'reveal' in your question makes me wonder to whom you are referring. If you mean, us the readers, then the above answer works because it is indeed what occured in the woods that Betty spoke of. This happened in the beginning of the Act when the girls were alone in the room.
Then by the end of the Act when other adults are in the room, she reveals to them that she saw Jacobs and Howe with the Devil. This we can assume is a lie or accusation.