What do you infer is the real reason Mary gives Elizabeth the gift in The Crucible?

Abigail has asked Mary to do this.  Abigail at this point has gained control of the town.  The people that she is accusing are being persecuted with little investigation.  Mary fears Abigail, as she has a right to do.  Although she tries to help the Proctors and tell the truth, she is quickly swayed by Abigail's intimidation.  Therefore, her reason is to obey Abigail.