According to the witness, one of the women had left the scene and returned with what appeared to be a boning knife. She then left after the fight. An ambulance was called to the scene.
A St Johns spokesman said the woman was treated at the scene for minor injuries.
While the victim was being treated in the ambulance the offender returned to McDonald's for the second time, and began screaming abuse at the victim, and at police.
She was then arrested.
McDonald's would not comment as it was a police matter.