After Mrs Kumar wrestled a metal pole off him, she tried to help her husband as he scuffled with the other defendant, who was wielding a knife.
"The younger boy was still standing in the doorway yelling out for us to give the money," she said.
"After they ran away I saw blood dripping down then I told him that he got hurt. As soon as I said he got hurt he looked at me and the blood started pouring out.
"I tried to cover his neck to stop the bleeding but he started collapsing."
The court adjourned to give the witness a chance to compose herself before being cross-examined.
She had to be helped from the courtroom by family members.
Afterwards, Mrs Kumar told the court she wished they had used the panic button behind the counter.
"I don't know why we didn't push it," she said.
The 13-year-old's lawyer David Niven in cross-examination suggested it did not happen because she and her husband did not feel threatened by the boys.
He said the couple believed they could get rid of the boys by simply threatening to call police.
"You had a choice about how to handle the situation, didn't you?" the lawyer said.
"But at that time we were just panicked. We didn't know what to do," Mrs Kumar told the court.
When asked to review her police statement the witness again broke down in tears and Justice Lang took another adjournment.
Earlier today Maria Pecotic, representing the older defendant, said the teenager did not mean to kill the victim.
"He did not act with murderous intent. We know Mr Kumar died but that fact, that consequence was never anticipated, planned or contemplated by [the defendant] ... nor did he intend an assault on Mr Kumar," she said.
Defence counsel for the younger accused also denied having the requisite intent the Crown needed to prove the charge.
"The defence asks you to carefully assess what was in [the younger boy's] head at the time when [his co-defendant] went into the dairy," Philip Hamlin said.
"The Crown can't prove he meant or intended for [the older defendant] to use a knife to assault, hurt or stab the shopkeeper."
Yesterday during the Crown's opening, prosecutor Kingi Snelgar described the sequence of events leading to Mr Kumar's death before playing CCTV of the incident.
Graphic footage showed the dairy owner's wife watch in horror as her husband bled to death on the floor of the shop they had owned for five years.
The knife wound, which severed Arun Kumar's jugular vein and was so deep that it left an imprint on his vertebrae, was allegedly inflicted by the 14-year-old boy during the botched robbery.
Mr Snelgar said it was the younger defendant who came up with the idea to rob the dairy on June 10 last year, and to take weapons to facilitate it.
The video showed the older defendant knock a phone out of Mrs Kumar's hands as she tried to pass it to her husband.
As she tried to wrestle the younger boy, Mr Kumar and the murder accused came together, eventually leaving the man in a pool of blood on the floor.
The trial in the High Court at Auckland before Justice Graham Lang and a jury of six women and six men is scheduled to last about a month.