A woman died after a police officer who wasn't qualified to drive over the speed limit engaged in "silly behaviour" and collided with her car at high speed, a coroner has found.

Constable Craig Simpson was driving a marked police car to a violent domestic situation involving a teenager armed with an axe in Armidale in northern NSW on February 9 last year.

Gillian Harman was killed in a crash in Armidale.

The 22-year-old was driving at 84km/h in a 50km/h zone through an intersection when he collided with another car driven by 48-year-old Gillian Harman.

Both vehicles rolled and Ms Harman was killed, Glebe Coroners Court heard on Monday.