A woman has been charged with impaired driving causing death after a fatal crash on Highway 407 near Oakville Saturday night.

According to police, 55-year-old Mary Sampson had a blood-alcohol level over 80 mgs when her Mazda 3 struck a Toyota Corolla head-on around 9 p.m. Police said Sampson was driving in the wrong direction at the time of the crash.

The driver of the Corolla had only minor injuries. His twin sister – 47-year-old Carol Grimmond of Windsor – was airlifted to Credit Valley Hospital, where she died of her injuries.

"The driver just had no time to react," said OPP Sgt. Dave Woodford. “When he saw [the car], it was the last second and when you are travelling at 100 km/h you have very little time to react.”

Sampson was not injured.

She was arrested at the scene of the crash and faces a number of charges including: impaired driving causing death, criminal negligence causing death and dangerous operation of a motor vehicle causing death.

Police are appealing to anyone who may have witnessed the accident to come forward.

"If you saw anything prior to the collision, or if you might know where that person who was out drinking had come from, we are interested in hearing, so we can piece it all together to see exactly what happened," said Woodford.

Witnesses are asked to contact the OPP at 905-841-5777.