Why were Mary Warren, Mercy Lewis and Abigail Williams gathered in Betty's room?
The girls assemble in Betty's room because the young girl has taken to her bed, sick with an ailment that has Reverend Parris very worried. Abigail is sent for the doctor, who diagnoses that he cannot find anything wrong with her. Betty won't wake up, she is actually pretending to be sick because she is terrified about having been caught in the woods the night before by her father.
Betty is so frightened that she is literally hiding in her bed with her eyes tightly shut so that she does not have to face her father and potential punishment which would be severe in the Puritan society that forbade such activities as dancing, music, except in church, and merriment on a casual basis.
News of Betty's illness spreads quickly since Abigail was sent for the doctor, it draws the Putnams to the Parris home. Their daughter, Ruth also lies in the same state, trance-like, unable to wake-up.
Abigail and the girls are really worried about what happened in the woods and are scared to death of the potential punishment that they will receive. They gather together to discuss their next course of action. Abigail demands that the girls stick to one story and insist that no witchcraft was performed in the woods. Even though they know that there was in fact spell casting going on, Abigail drank blood as a charm to wish Elizabeth Proctor dead.
Abigail comes up with a strategy and threatens the other girls to follow her lead. She says that she will kill anyone who does not obey her instructions. She is a very forceful character, intimidating the other girls into following whatever she does.
Reverend Parris has sent for Reverend Hale from the town of Beverly, he is an expert on witchcraft. Everyone in the room is eager for Betty to return to health. All the members of the congregation have assembled in the church to pray for Betty. It is during this prayer service that Abigail threatens Betty and the other girls to keep their mouths shut and only act as she acts.