She died in Starship Hospital eight months later.
Detective Sergeant Steve Brewer, head of the police North Shore Child Protection Unit, said he was satisfied with the outcome, despite Ikamanu being found not guilty of murder.
"It's very hard for a jury. There's all sorts of things that they have to consider. I think Seini got justice today."
Mr Brewer investigated Seini's death and said the case had been difficult for all those involved, especially the child's mother, Sela Taufu.
"(Seini) was ill for a very long time and I've been to see her mum a number of times when she was at the bedside vigil at Starship, and when she was in palliative care at home.
"It's been a long two and a half years to get to today,'' said Mr Brewer.
The officer, who has two young children , said he had been personally affected by Seini's case.
"It's been a very sad case ... especially how long it's taken Seini to pass. She carried on like a little trooper."
Ikamanu was looking after his children at their Beach Haven home when Seini was injured. His wife was at work.
The trial heard he gave different explanations for their cause. On separate occasions he told police her brother pushed her down the stairs, he had thrown her against the wall and that she fell and hit the wall after he grabbed her hand.
Ikamanu's lawyer Simon Lance said much of the prosecution case was "Crown theory" rather than evidence.
"Not all deaths are a murder, and this is one of the cases where it is not."
