Ian Pullen, 43, was found dead on the side of the road early on September 29, 2018, at Glenridding, near Singleton.
The young father, who worked as a firefighter pilot, had been brought in to help fight bushfires in the area.
NSW Police arrested a 30-year-old woman on Monday morning at a home on Dominion Avenue in Singleton.
The woman is the second person charged with murder over the suspicious death after the arrest of a 29-year-old man at Newcastle Police Station last week.
Police will allege in court the man was driving a white Toyota Hilux utility when Mr Pullen was hit, and that when the vehicle returned a short time later and the man and woman struck Mr Pullen in the head with an object.
The woman was refused bail to appear at Muswellbrook Local Court on Tuesday.