Mr Dalton reportedly punched a door, and as there was nowhere to keep him at the unit, he was referred to the police station in Apia.
According to Ms Dalton, police were told by hospital staff the man was not a prisoner and needed to be looked after. Instead he was taken to Tafa'igata Prison.
On Boxing Day, as his family were getting ready to visit Mr Dalton at the prison, police arrived at their home and told them he had died.
Mrs Wilson was given the bad news at Faleolo Airport after flying in from Auckland. She said the family was able to see Mr Dalton's body at the hospital.
She told the Observer her son had brain fluid coming out of his ears and bruises all over his body.
"I know he banged his head on the wall, because people do that when they're in that condition; but if you see someone doing that, you don't just let them - you try and stop them from hurting themselves."
Assistant Police Commissioner Le'aupepe Fatu Pula said Mr Dalton's death was "an alleged suicide", the Observer reported.
Le'aupepe said Mr Dalton was transferred from the police station in Apia to the prison as the station was "too busy".
The cellblocks at Tafa'igata Prison have gallons of water for the toilets, he said.
"It is alleged that Mr Dalton jumped inside the gallon head first, and that is why we suspect it was a suicide."
Mrs Wilson said it was dangerous to assume how her son had died.
"I don't know if it was another prisoner or one of the staff. I think at the back of it all is a lack of understanding of mental illness," she told the Observer.
"One thing I'm very sure of is that my son did not take his own life."
Mrs Wilson described her son as "a gentle and sensitive person with the most beautiful soul".
She said her son's death highlights the need for better mental healthcare services and facilities in Samoa.
Mr Dalton's body was flown to back to New Zealand early Monday morning and her family were today preparing for his tangi. Mrs Wilson said the New Zealand Coroner is investigating the death.
- nzherald.co.nz