I am a lawyer in CT and practice in this area of the law.  If your mom no longer wants to work there, then sue the employer for negligence (employer owed a duty of care to your mom to provide a safe working environment and knew the co-worker had a kinfe that could harm someone and failed to do anything to prevent it).  You can also sue the co-worker for assault/battery.  I suggest retaining a lawyer asap to file this action.  I suggest waiting till the lady is prosecuted so you can use the conviction or guilty plea against her in the civil case.