Inside the bus she failed several more tests which Constable Anthony McFarlane told the inquest he put down to nervousness.
Moments later she collapsed and slid off the chair, hitting her head on another seat as she fell to the floor.
Mr McFarlane called his colleagues for help and an ambulance was requested but before it could arrive, six minutes later, Ms Gilbertson's lips had turned blue, her face went pale and her pulse became faint.
St John staff spent 37 minutes trying to resuscitate the South African immigrant, who had moved to New Zealand six months earlier to be reunited with her family.
At the inquest in the Hamilton District Court, forensic pathologist Dr Simon Stables said he believed Ms Gilbertson, had become highly stressed and had heart disease.
"I think it is sufficient in the circumstances, especially coupled with the extreme stress, that this has been enough to tip the balance where she has suffered a quite significant arrhythmic heart rhythm problem, and that's led to her death."
Dr Stables said Ms Gilbertson had enlarged heart muscles requiring more oxygen and a borderline severely narrowed coronary artery, meant when her heart went into arrhythmia because of the stress, she couldn't get enough oxygen.
Dr Stables recommended all booze buses carry defibrillators in case of such emergencies.
Despite the tragedy siblings Ian Gilbertson, a Cambridge GP, and Marion Morris, a nurse at Waikato Hospital, said they did not hold police responsible for Ms Gilbertson's death.
Dr Gilbertson thanked police and ambulance officers for the attempted resuscitation of Ms Gilbertson.
But he said the family suggested recording devices would "protect the police and the public" in similar situations.
He said the family was relieved to know Ms Gilbertson was treated with respect during the incident, and that an autopsy proved her well under the legal alcohol driving limit.
Coroner Gordon Matenga reserved his decision.
