Instead, the 57-year-old said she had been prepared to give her nephew $150,000, but that he had insisted he was owed half, as both names were on the ticket.
During the cheque presentation, Ms Reddick unleashed a shocking attack on her nephew, telling reporters he "didn't deserve" the cash.
"See you in court," the CBC network reported the woman as saying at the event.
"I bought the ticket. Now he's trying to lie and say I said 'split' the winnings.
"I put his name on the ticket for good luck because he's like a son to me — he was. He was lucky, but not for half a million dollars."
Ms Reddick said she was "heartbroken" by the feud.
"He's dead to me," she said.
"I'm heartbroken because I don't think he should have got half of the money … I always put Tyrone's name on the ticket for good luck. We had no discussion of money.
"Tyrone is getting nothing from me. I'm taking him to court. It was my ticket.
"It's just for the principle. We were so close. He broke my heart. He broke it. People go crazy when it comes to money."
Ms Reddick has also reportedly disowned her brother, Mr MacInnis' father, as she believes he wants to use his son's winnings to buy a new truck.
According to a lottery official, the prize had been split down the middle as there were two names on the ticket — meaning each relative was awarded a $C600,000 ($A615,000) cheque.
The official told CBC is was a standard practice that has been approved by the provincial gaming commission.
"I didn't expect anything like that to happen," the official said. "I'm a little bit disappointed."
The Margaree Chase the Ace lottery had been organised as a fundraiser for two volunteer fire departments in the town.
After posting a photo of the warring winners on Facebook, the lottery's page has been inundated with opinions from strangers regarding who was in the right.
"Yes, she put his name on the ticket, but I believe her about not splitting the winnings, although she's going to lose the case," one woman posted, while another wrote: "Really? 1.2 million and you are looking sour and upset? I don't think any amount would make that lady happy."
Many have criticised Ms Reddick for her "greed" — although others pointed out only she and her nephew would ever know the truth of their arrangement.