His sentencing is set for November 25.
Edwards had an "active part" in the driving, the Crown said in its closing arguments yesterday.
However, his counsel said the Crown had failed "by a wide margin" to prove his liability, saying he never encouraged the driver.
The Invercargill nurse died in 2018 when the car she was in with her husband and two children was T-boned by a Subaru driven by Dejay Rawiri Kane.
Kane was convicted last year for driving at an estimated speed of 124km/h with a blood-alcohol level three times the limit.
Crown prosecutor Mary-Jane Thomas said in her closing address Edwards "knew and chose" to be in the car.
He had "every opportunity" to not return to the car when he was at a friend's house but he chose to, she said.
"The Crown says Emma Bagley would be alive but for the actions of the defendant on December 7.
"His presence and remaining in the vehicle ... in fact encouraged the driver," she said.
"This defendant wasn't an uninterested spectator, sitting in the vehicle ... he was having a ball, he was enjoying himself."
Thomas believed Edwards "overplayed his level of intoxication".
She said Edwards' evidence that he had "blacked out" for most of the night due to alcohol consumption should be dismissed.
Defence counsel Fiona Guy Kidd QC said Edwards was "telling the truth".
"If he was lying about these blackouts, wouldn't he have come up with better lies?
"Wouldn't he have denied driving in Windsor?
"Wouldn't he remember what he had drunk at Hansen's?
"But he didn't," she said.
Guy Kidd said none of the witnesses or any evidence verified Edward was in the car when Kane was driving dangerously earlier that evening.
Edwards should not be considered guilty if he was "likely" or "probably" involved; the jury should be sure all the elements of the charge were proven, she said.
There was no intentional encouragement of manslaughter, reckless driving or dangerous driving by her client, she said.
"It doesn't make sense ... that the front-seat passenger would intentionally do this given it would put his own life and others in danger."
Justice Mander summed up the case and retired the jury, which started deliberations yesterday afternoon.