Jesse and Samantha Shortland were in Hokitika for the funeral of Jesse's father, leaving at about 12.30pm on October 8.
Liebl was driving north on the Dipton-Winton Highway (State Highway 6) before colliding with a Honda Odyssey driven by Jesse Shortland driving South at approximately 9.38pm.
Liebl and Jesse and Samantha Shortland died in the collision. The Shortlands' two children, 2-year-old son Heath and 8-month-old daughter Skylar, survived the crash.
A scene examination revealed Liebl had crossed into the other lane and was the "primary reason" for the crash, although the reason why she did this was unknown. It was unlikely Liebl had been travelling on the wrong side of the road for some time.
Vehicle data revealed Liebl's vehicle was travelling at 134km/h five seconds before impact, before last-second braking reduced the speed to 73km/h.
The Shortlands' vehicle was estimated to be travelling at 119km/h.
The coroner said both drivers were travelling at "excessive speed" and fatigue had "likely played a significant factor in this crash".
"Both Ms Liebl and Mr Shortland had driven significant distances," said Coroner Robinson.
A toxicology report also found cannabis and tetrahydrocannabinol in Shortland's blood, although the coroner could not determine what influence, if any, this had on his driving.
However, the coroner found the "Drive Safe" form Liebl filled out at Thrifty Rentals Queenstown was "wholly inadequate".
"There is no effective evaluation of the person's ability to drive in New Zealand, nor of their knowledge of the road rules."
He encouraged car rental companies to introduce some "qualitive assessment" into the process for the determining whether to rent a vehicle to an overseas driver.
