A woman who drowned her four-year-old daughter and burned her body in what she saw as a religious sacrifice has been found not guilty of murder by reason of insanity and will be detained in hospital.

Carly Ann Harris, 38, drowned Amelia Brooke Harris in the bath at their home in south Wales after suffering a mental breakdown that led her to believe she was saving the world, Newport crown court heard.

The jury took an hour to reach the not guilty verdict on Monday after hearing that psychiatrists for both the prosecution and defence agreed Harris had paranoid schizophrenia. She was given a hospital order.

The judge, Simon Picken, told her: “A richly promising girl met her death at the hands of her mother and in the most horrific manner. I am satisfied that you are suffering from a mental health disorder, namely schizophrenia.

“The intention is that as soon as possible you will be transferred to an appropriate clinic close to home. The most suitable method is me making an order under section 37 of the Mental Health Act 1983, and that is necessary to protect the public from serious harm.”

Speaking outside court, Harris’s mother, Jacqui Harris, said: “I think it is the right verdict and the judge was decent and kind. He has done the right thing. I’ve gone beyond tears. She is my daughter and I am devastated and I have lost my daughter. She is not a monster. She is the salt of the earth.”

During the two-day trial, jurors were told there was no dispute that Harris had killed her daughter or about the events leading up to the incident.

Amelia’s teenage brother found her body wrapped in a sheet on a table in their garden in the village of Trealaw, near Tonypandy, on 8 June.

A neighbour, Megan Griffiths, saw Harris standing in the front garden looking “dazed”. Harris told her: “God will be with her. The angels have taken her.” When police arrived at the scene, Harris told them: “The angels told me to do it. Just arrest me. It’s OK.”

One of Harris’s two sons said his mother had not been well for six weeks before the incident, the court heard.

A Home Office pathologist, Dr Richard Jones, concluded that Amelia had died from drowning and was already dead when she was set on fire.

Harris had been taking small amounts of amphetamines in the period leading up to the incident, but experts agreed she had not been suffering from drug-induced psychosis.

Dr Arden Tomison, a psychiatrist, diagnosed Harris with schizophrenia and said that at the time of the incident she was suffering from an “abnormality of mental function which substantially impaired her ability to form a rational judgment”.

He said she appeared to have experienced “paranoid and religious delusions” and believed she had to kill Amelia to save the world and was being tested by God, who would then return her daughter to her.

Tomison said that when he examined Harris as recently as a month ago, she was still firm in the belief that she had had to kill her child in order to protect her and save the world.

He said that despite efforts by doctors at a secure institution to get Harris’s psychosis under control, she was still sure she had been instructed by God.

Another psychiatrist, Dr Philip Joseph, agreed that Harris had suffered from schizophrenia following a urinary tract infection in 2014. Joseph also said he believed that Harris’s abuse of amphetamines may have triggered a psychotic episode.

Kate Brunner, defending, said: “In taking her daughter’s life she destroyed her own life and brought unimaginable horror to her friends and family.”

A spokesperson for Cwm Taf safeguarding board said: “This was a tragic incident which shocked the community. We would like to take this opportunity to pay tribute to Amelia’s family who have acted so bravely since the incident occurred.

“We would also like to thank emergency service workers who worked so professionally when they were faced with very difficult scenes. We will continue to provide the family with the help and support that they need. Amelia, of course, will not be forgotten.”