Why can't Mary faint when she is asked to? What does this suggest about the groups dynamics?

When she is asked to show the court how she pretended to faint, she can not do it, explaining that she has “no sense of it now”. She continues by telling them that she can not do it for the same reason that she was no longer crying out against people. Following this episode in court, the other girls begin to accuse Mary of witchcraft and when this happens, Mary gives up on trying to tell the truth and then accuses John Proctor of being a witch.