In The Crucible, why does Mary's explanation, that earlier she had been pretending, come to nothing?

John Proctor finds out that his wife is to go before the court and he implores his servant Mary to go before the court and admit that she and her friends had lied. But when Mary goes into the court to confess that she and the other girls were only pretending and that she had never seen the devil. But as she had predicted when she said “They’ll turn on me! I cannot!” her friends did in fact turn on her. Her friends then pretended that Mary is sending the spirit onto them in the courtroom. John panicked and said that the only reason Abigail was targeting Elizabeth was because they had been involved in an affair and Abigail was jealous. In an erroneous effort to shield her husband, Elizabeth denies the affair took place which leads the court to think John was lying. Mary was scared that everyone would think that she was the witch and she in turn, turned on John Proctor and said that the one who made her lie and that he, in fact, was the witch.