"There was evidence that came out [at trial], and I think the judge indicated, that it was impossible for Jonathan to do it, and also that the police didn't really have any evidence to charge him," she told APNZ.
She said the Dalton family, many of whom were still in Samoa after attending the trial, were glad "someone has not been afraid to stand up and tell the truth".
"I think that from what the judge said, the prison guards were the only ones with the keys that had access in and out of the cell," she said.
The family lawyer was working on what action to take next.
"As a family, we just want the truth to be told and we're glad that this decision yesterday has brought some justice for my brother," she said.
"I never saw him as a mental health patient, he was always a brother, an uncle, a son."
Mr Dalton was a "well loved" member of the family, who had been a great help looking after his father who suffers from dementia.
"Everyone misses him terribly," she said.
"I'm still in shock and quite traumatised by seeing him hours before [his death] and having to see his body the way it was the next day."
Ms Dalton also criticised the way her brother's mental health episode was handled by local authorities, when he lost access to his medication while on holiday in Samoa after a cyclone hit the Pacific Island nation. He was put into a prison cell when medical staff were unable to calm him down.
"I think that made him worse," she said.
"He was given an injection and put in a prison cell. Someone should have been there monitoring him the whole night, or they could have made contact with us and we would have came and been with him."
