A 16-year-old girl who set fire to her home when her mother was asleep in bed and claimed that voices made her do it has been sentenced to four years detention.

The girl, who cannot be named because of her age, had threatened to kill her mother and medical experts believed there was still a risk of “posing significant harm to others, particularly her mother”.

This was said at Caernarfon crown court where it was revealed “the catalyst for the fire was a comment about washing up.” She pleaded guilty to arson with intent to endanger life and Judge Huw Rees ordered an extended licence period of three years.

Matthew Curtis, prosecuting, said the girl’s mother had been alerted by a smoke alarm while having a lie-in after her partner had left for work in the morning from their rented semi in a Gwynedd village.

When she went downstairs there were two sofas on fire in the living room. She dashed upstairs to see if the girl was in her bedroom but it was empty and she dialled 999.

CCTV showed the girl had left the house at 7.34am and she was found two miles away, “looking jittery and scared” and in clothing not suitable for a cold morning.

“She said she was worried about police and other people coming after her and admitted she had set fire to the house… saying the voices made me.”

Mr Curtis said : “Doctors said she was not suffering from mental illness although she had mental difficulties.” She had not met the criteria to be sectioned.

A fire investigation revealed deliberate ignition to the ground floor living room below her mother’s bedroom. Without a smoke alarm there was little doubt that the mother would have been trapped in the bedroom, the barrister added.

The owners of the property, worth up to £130,000, were a London couple who bought it as their intended pension pot and had rented it out. Damage was put at up to £50,000, the house was still uninhabitable but because the damage was malicious insurers would only pay a small proportion of the cost.

In a statement read to the court the mother referred to the girl as “my beautiful daughter” and said her ‘episodes’ had been heartbreaking. She had to take time off work because of their frequency. The mother said : “I want my daughter to get the help she requires. I still love my daughter, that will never change. Do I blame her? – no I blame her state of mind.”

Richard Edwards, defending, said the girl had been “very open and forthcoming during interviews with various professionals” about feelings of anger and resentment which had built up over the years.

He told the court : “It was a comment about washing up which seemed to be the catalyst. She’s a particularly vulnerable young person. It’s clear she needs assistance and guidance from professionals.” She was bright academically and now living in a secure children’s home in the north of England where she was engaging well, receiving help and awaiting GCSE results.

The girl was expressionless in the dock as she was sentenced. Judge Rees said she would remain at the home until she was 18.

The judge said alcohol had been used as an accelerant in the fire. Her mother had drifted back to sleep “and she only roused when she became aware that smoke had activated the fire alarm. She thought she could smell toast burning but quickly realised the house was on fire.”

The judge said three cats, household pets, had died and totally innocent people had been affected “by the wanton destruction.”

On one occasion last year the girl had entered her mother’s bedroom with a knife, shaking and crying and speaking of voices.

Professionals had concerns that she could “pose significant harm to others, particularly her mother.”