Two teenage girls were arrested not long after, with the third arrested a day later.
The woman suffered serious injuries and was admitted to hospital after the attack.
A Gisborne-based relative told the Herald last month that her grandmother had been viciously attacked.
The family had appealed for information about what happened while they anxiously waited to learn whether the 90-year-old had suffered a brain bleed.
"There was a knock at the door, so she answered it," the relative said.
One of the two women at the door claimed she badly needed to use the toilet, so the 90-year-old woman obliged and let the pair into her Bath St home, she said.
But while her back was turned the elderly woman was struck over the head with an object before more blows followed, she said.
The beating included being kicked while she was on the floor, she said.
She had to crawl to a phone to dial 111, she said.
"She nearly died," the relative said.
"She's a teeny little old lady, how could someone do that?"
St John transported the woman to Palmerston North Hospital.
The relative said her grandmother's purse was missing after the attack.
Manawatu Area Investigations Manager Detective Senior Sergeant Craig Sheridan confirmed items were taken from the house and police had asked for the public's help.