Kuka is charged with manslaughter for failing to seek medical treatment for Nia and failing to protect her from violence.
Kuka allegedly told Dr Kelly that Nia had been well when she got home from work on July 20 last year, but was unresponsive when she bathed her during the night after Nia wet the bed. She was unable to wake Nia next morning.
In spite of this, the little girl wasnot taken to hospital for another day.
Dr Kelly examined Nia at Auckland's Starship hospital after she was transferred there from Rotorua Hospital on July 22.
He said she was comatose, could not breathe on her own, and showed no improvement at any stage during the 12 days before she died.
Nia had a subdural haematoma, or bleeding between her brain and skull, which caused her brain to swell.
Dr Kelly said the injury was likely to have resulted in coma symptoms "immediately and certainly within minutes, at most an hour or two".
He said children with subdural haematoma could be treated, but "the best chance for a best outcome is to see that child as soon as possible".
Kuka allegedly told Dr Kelly that Nia had fallen and hit her head while "playing rough" with someone at home. But the Crown alleges brothers Wiremu and Michael Curtis put her in a coma by kicking her in the head while Kuka went out for half an hour after coming home from work on July 20.
In written statements read to the court, Michael Curtis denied the allegation, telling police, "That's all shit. No one kicked her."
Wiremu Curtis said Nia had been on his shoulders and had fallen, and her head hit the floor.