Nia died in Auckland's Starship Hospital on August 3 last year.
On October 9, in her fifth and final video interview with police, Kuka changed her story from an earlier interview and admitted she saw Nia being subjected to a wrestling move called a pedigree at the Frank St house.
She said the move involved Nia's head being placed between an adult's legs and her body slammed upside-down on to a mattress.
Kuka admitted she made no attempt to stop the wrestling.
"I wanted to go somewhere. I just walked out the door."
Asked why she had not taken action, Kuka said: "I turned a blind eye, thought Wiremu would never hurt [Nia], never hurt [her], and yes, I was in love with him."
Kuka also said she had seen Nia being "whacked" by Oriwa Kemp, who is the second person charged with Nia's manslaughter.
"I'm not saying I never ever smacked her, but I never smacked her like that," Kuka said.
"What did she do?" the interviewing officer, Detective Sergeant Garry Hawkins, asked.
"It was just the way she used to whack, whack, whack Nia," Kuka replied.
"How did she whack her?" Mr Hawkins asked.
Kuka: "With [an] open hand across the face, across the head, across the back.
Why? Because she was ugly."
Mr Hawkins: "Did they say that?"
Kuka: "Oriwa says that a lot."
Kuka said Nia would cry when hit and the other accused would tell her to shut up.
"What would I do? Nothing, just sit there," Kuka said.
Asked why she did not take Nia away from that environment, Kuka said she would argue with the other accused but they always had excuses, telling her: "We look after her. You're at work. Where are you?"
She had thought about taking Nia to safety "but I would also have taken Wiremu".
"I wouldn't say that I didn't care what was happening to my daughter, but yeah, my loyalties were to Wiremu."
Kuka was 34 and Curtis was 17 at the time.
They had been together a few months.
Kuka said she never saw anything done to Nia by Wiremu's brother, Michael, who is jointly charged with Nia's murder, or by her nephew Michael Pearson, the third person charged with the 3-year-old's manslaughter.
"He was my heart," she said of Pearson.peNia was allegedly kicked in the head by the Curtis brothers while Kuka and Kemp were out for about half an hour on a Friday evening, and lapsed into unconsciousness.
Kuka said her daughter was awake when she left, but asleep when she got home, and had failed to wake when she bathed her about 4am on the Saturday.
Kuka said she wanted to take her to hospital or a doctor, but "I was told not to".
"By who?" Mr Hawkins asked.
"By all of them. Michael [Curtis], Wiremu and Oriwa."
She said they told her, "She'll be alright, we'll look after her. She just needs a good sleep."
Kuka gave a lengthy pause when asked why she had not taken Nia to hospital during the whole of the Saturday, when a 21st party was held for Michael Curtis at the house.
"I didn't want to know what happened," Kuka said. "I listened to Michael and them...[saying] 'she'll be fine'. Deep down I knew she wasn't fine."
She admitted hardly checking on Nia during the day, saying she could not stand going into the bedroom where she was lying because she knew Nia was not right.
"But I didn't do nothing about it. Nothing. And it was too late on Sunday. And if I had done something on Friday she may still be there with me, but she's not."
Nia had asked to come with Kuka when she went out on the Friday to drop a car to her brother, but Kuka had refused, telling her she would not be long.
"She more or less threw herself like, 'Please Mum, take me'."
Asked at the end of the 20-minute interview is she had anything else to say, Kuka paused, upset, and repeated: "Why did I not do nothing? Why didn't I seek medical advice? ASAP? Why?"
She said she had had "a big change of mind" after finding out "what actually happened" to Nia following an autopsy on her body.
Kuka said she accepted she was going to be arrested and charged.
