A home detention term was imposed by Justice Whata, however, the length of the sentence will be determined at a later date.
The horrific case of elder abuse was revealed by the Herald last week.
The 42-year-old niece, who has interim name suppression, will also be sentenced later this year after pleading guilty to the same charge.
She had taken sole responsibility for the fulltime care of her aunt in April 2017, court documents read.
Crown prosecutor Yelena Yelavich said today she was an "extremely vulnerable elderly victim".
The 89-year-old was relocated to her niece and her husband's Auckland home, where the pair were supposed to care for her due to her acute dementia, incontinence, and immobility.
A resthome was not an option for the family due to language difficulties, the court heard, and the niece's husband would care for the elderly woman during weekends.
In November 2017, however, the niece's husband notified his wife of her aunt's condition.
She was found to be unresponsive, court documents read.
The niece then called an ambulance and paramedics arrived to a horrific scene.
In the lounge was the 89-year-old, lying naked and underneath a blanket on a sofa. When ambulance officers pulled back the blanket they discovered her body appeared to be fused to the couch.
She was also covered in urine, faeces and pus, which had formed an adhesive gluing her to the sofa.
Ambulance staff could not separate her from the couch without causing further pain and injury, so they were forced to cut the couch away before taking her to Middlemore Hospital.
The sofa material, however, remained bound to her body and upon reaching hospital, medical staff found the woman in a life-threatening condition.
She was suffering from bacteraemia, dehydration, and low albumin - a protein made by the liver.
Police were also notified and began investigating.
The 89-year-old had several stage four pressure ulcers to her body.
Stage four pressure ulcers are the most severe pressure ulcer formation and are characterised by full thickness skin loss, tissue necrosis, and damage to muscle, bone, or supporting structures, court papers read.
One pressure sore was down to the bone.
A subsequent medical examination has also revealed a bone infection, the court heard today.
Medical staff further noted her skin was broken down, and had dry old skin peeling away from parts of her back.
They found she was also "clearly underweight" and had a fixed flexion of her arm and right hip which may have taken weeks to develop.
The doctor who examined her couldn't say how long it would have taken for these injuries to develop.
But he did say it would've "taken more than a few weeks of lying on her back and left side to sustain this degree of pressure sores".
The niece took responsibility for the condition of her aunt and told police it was the result of her "own stupidity" and she should have called for help sooner.
Her husband, who was supported in court today by a church minister and two close friends, upon reflection thought he too should have called for help sooner.
The court heard the husband had noticed "abnormalities" to the elderly woman two weeks prior to an ambulance being called but said he was unaware of the ulcers.
Justice Whata told the man: "You are clearly remorseful."
The judge also said he was a "good, giving person" who had not followed his instincts and posed no threat of reoffending.
