"While she was burning ... she repeatedly told him, 'It was the gas, it was gas in my house'," Ms Wehi said.
"She got home, smelled the gas, unlocked the door and turned on the light, and boom - the whole house blew up."
The property's owner, Peter John McLeod, 73, pleaded guilty yesterday in Whangarei District Court to undertaking an unauthorised gas fitting, failing to take all practicable steps to ensure that gas appliances were safe and completing gas work where not authorised to do so.
A specialist fire investigator said the explosion resulted from a faulty gas appliance in the kitchen.
The charges were brought by Energy Safety, part of WorkSafe NZ, and carry a maximum penalty of two years in prison or a $100,000 fine.
McLeod will be sentenced next month.
Ms Wehi said her niece, a former Child Youth and Family state ward, had grown up in South Auckland but moved to Northland about two years ago.
She had a good job with a trucking company and had only tenanted the rental a week earlier so her eight siblings and their children could visit - "to bring all her family back together".
On the night of the tragedy, Ms Wehi-Jack had just arrived home from work. The force of the explosion rocked neighbouring homes.
She was rushed to Northland Base Hospital but transferred to Middlemore Hospital where she died surrounded by family less than 24 hours later.
"Her body started to shut down. It was very sad. None of us wanted to see her suffer.
"We knew she wasn't going to come through it. She was totally bandaged. Everything on her was weeping and bloated. The skin was falling off her hands. Her hands were totally burnt like skinny little branches off a dried tree."
Ms Wehi welcomed today's guilty pleas.
"He's got to live with the consequences of his actions for the rest of his life. He can go to prison and it still won't erase that from his memory."
McLeod had never contacted the family to apologise, Ms Wehi-Jack said.
"That would have shown he was remorseful. Nothing like that came from this man."
Her niece's death was a lesson for other landlords looking to cut corners with cheap DIY work.
"If there's anything to do with gas or electrical, do it properly [because] at the cost of someone's life, it's not worth it."
And though the justice process is nearing completion, the family's profound sense of loss will endure.
"We're never ever going to see her get married, be pregnant, having a baby and the excitement on her face.
"For Maori families that's a generation of our family line gone. It can never come back."
