A number of large household items were packed on to the truck that were about level with the top of the cab.
Josie Takimoana was on the back of the ute with an 11-year-old girl while Megchelse was in the cab with two girls aged 8 and 15.
When a number of items fell off the ute on to the road the young girl became frightened and opted to ride in the front with the three others.
Takimoana remained on the back and sat on the roof of the ute facing the rear of the vehicle.
Police said Takimoana then lay down on the roof of the cab and leant over the windscreen and looked into the cab.
As she did so Megchelse drove round a medium right-hand bend.
Takimoana slid off the left-hand side of the roof and slammed headfirst into a steel barrier on the side of the road. She suffered serious head injuries and died at the scene.
When police breath-tested Megchelse recorded 600 micrograms of alcohol per litre of breath and said he had drunk four bottles of beer about 90 minutes before driving.
Takimoana's father spoke briefly in court and confirmed his family has agreed to a restorative justice meeting with Megchelse.
He said he did not blame Megchelse but his daughter for what happened.
The man said it was hard farewelling his daughter over the holiday period and that he wanted Megchelse to spend time with his children.
Megchelse was remanded in custody for sentencing on March 29.