Mrs Taufu wept as she told the court her daughter had bruises on her face in the days leading up to the incident in March 2010.
She said Ikamanu and her daughter had both said Seini had got the bruises after falling over while playing.
Mrs Taufu said on the day of the incident, her daughter had started to cry when she said she had to go to work.
"I told her because her birthday was coming up, Mummy is going to work to get some money to buy her a bike,'' she said through tears.
Mrs Taufu confirmed to Crown prosecutor Tiffany Robertson that her daughter had been healthy on the day the injuries were suffered.
But later that evening she got a call at work from her husband, who said Seini was having a seizure.
"I asked him what happened and he said to me that he was talking to her and all of a sudden she had a seizure.''
Mrs Taufu said when she arrived home she found her husband running a shower for Seini who was lying on a towel.
"I lifted her eyelid to see if she responded. She never responded.''
She said she didn't ask Ikamanu any more questions because she was concentrating on her daughter.
The two-year-old was rushed to Starship Hospital, where doctors found bleeding on her brain.
Eight months later, following surgery, Seini died in hospital.
Earlier the court heard from Crown prosecutor Phil Hamlin who said Ikamanu changed his story when speaking to authorities in the days following Seini's admission to hospital.
Mr Hamlin said Ikamanu told one police officer that Seini and her brother had been playing outside when Seini fell down the steps.
"And - to use my words - out of the blue, Seini began to have seizures.''
Ikamanu later told another police officer a different story.
"He told the police officer that he threw the child against a wall in the loungeroom of the house.''
A short time later he told the officer that he had been holding the girl's hand and they had both let go and she had fallen against the wall.
Ikamanu's lawyer Simon Lance said much of Mr Hamlin's opening address was "Crown theory'' not evidence.
He said an example of this was evidence about bruising found on Seini's chest.
"What we know is that Mr Ikamanu attempted CPR. Doctors will say the bruising on the chest is consistent with someone attempting CPR.''
He said Ikamanu was there on the night - not Mr Hamlin.
"Not all deaths are a murder, and this is one of the cases where it is not.''
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Timeline of events, according to the Crown
April 14, 2007: Seini is born
September 2007: Seini moves to Tonga to stay with her grandparents
July 29, 2008: Seini's brother Manamoui is born
January 29, 2010: Seini returns to New Zealand to live with her parents
March 22 and 23, 2010: Seini's mother notices her daughter has bruises on her face, a red eye and bruises on her back
March 24, 2010: Seini is taken to hospital with fatal head injuries, a broken shoulder and shattered pelvis
November 30, 2010: Seini has neurosurgery
December 6, 2010: Seini dies in Starship Hospital