The group hired two rental cars and travelled the country with at times three in each vehicle.
On the morning of the crash, the group had left their hotel in Te Anau with the intention of walking the Milford Track.
Mrs Wilder was a back seat passenger in the 2011 Toyota Corolla she was travelling in.
The vehicle had travelled across a straight section of open road in an area surrounded by beech forest and native forest. The road gradually rose with an easy, gradual right bend, Coroner McElrea said.
As the vehicle entered the bend it left the left-hand lane, travelling off to the right and across the centre line.
It then entered the opposing northbound lane and left the road, becoming airborne and colliding with the trunk of a large beech tree.
Mrs Wilder was not wearing a seatbelt and due to the impact of the crash, was propelled forward and into the rear of the driver's seat. She died at the scene.
In an interview with police, the car's driver Ms Shelv said she couldn't explain what or how the crash happened.
She told police that when she got out of the car and saw the wheel, she thought the tyre had blown.
A police investigation found that not to be the case.
Dunedin Serious Crash Unit Senior Constable Trevor Buchanan told the inquest that had Mrs Wilder been wearing a seatbelt, she would have survived.
"She would have had injuries, but nothing like the ones she suffered."
He noted that the driver, who was wearing a seatbelt, sustained survivable injuries while being closer to the tree. The driver also benefited from an airbag.
Mr Buchanan said that in his opinion the driver went to sleep during the negotiation of the right hand bend and only woke up due to the car impacting either small saplings or the large beech.
He cited the lack of braking or steering input to support his reasoning.
"This supports all international studies into sleep being a factor in a crash such as this."
The car's speed would have been in the vicinity of 70 to 80km/h at the time of impact, Mr Buchanan said.
Coroner McElrea said the importance of wearing a seatbelt at all time was illustrated by "this preventable death".
