Two 15-year old girls who tortured a vulnerable woman to death have been sentenced to a minimum of 15 years’ detention. Angela Wrightson, 39, was beaten in her home, in Hartlepool for almost nine hours, suffering more than 100 injuries, before she was killed by the two girls.

The pair – who were just 13 and 14 at the time of the attack, and cannot be named because of their age – were found guilty of her murder earlier this week after an eight-week trial.

On Thursday a judge, giving them life sentences, ruled they should be detained for a minimum of 15 years.

Wrightson, 39, who was described as vulnerable and who was an alcoholic, had befriended the two girls, buying them alcohol and sweets from the local shop. But the girls turned on her, torturing Wrightson in her home using household objects including a television set, coffee table and wooden stick.

Wrightson was made to plead for her life as they “forcibly restrained” her; the girls only stopped the assault to pose for pictures, which the younger girl – said to be obsessed with her phone – sent to friends on the social network Snapchat with the caption “Nah xx”.

They were caught on CCTV leaving Wrightson’s home at around 11pm and returning at 2am, when they continued to torture her for another two hours. They finally left the house at 4am and even called police to give them a lift home when again they took a picture and shared it on Snapchat.

Both girls denied the murder and failed to show any remorse during the Leeds crown court trial, at which they tried to blame each other. The older of the two admitted manslaughter while the other said she did not encourage or take part in the violence.

It emerged the pair had absconded from care homes 18 times in the 30 nights before they battered Wrightson to death.

In mitigation, Jamie Hill defending the older girl, referred to as Girl A, said the violence inflicted against Wrightson was “born out of childhood stupidity” and the girls were “clearly out of control”.

Hill argued that the youngster, who was 14 at the time of the murder, was suffering from a mental disorder and had not intended to kill Wrightson.

He said: “Alcohol was a common thread which drew these girls to Angela Wrightson’s home. The two girls were deeply troubled children who found themselves in the sad, unpredictable world which had been Angela Wrightson’s refuge.

“It is difficult to rationalise what happened. One life has been lost and several others have been ruined. This child is not one that was evil but one that was damaged who put herself in a strange place. Whatever the trigger for the violence she was not a fully functioning person at that time in her life.”

Wrightson, who weighed just six-and-a-half stone, was found dead in the blood-spattered front room of her terraced home in Stephen Street, Hartlepool.

The two teenagers befriended the frail alcoholic because she would buy them cider. But on 8 December 2014, they turned on her.

Using multiple weapons for the “brutal and sustained” beating, they “heaped further indignities” on their victim by stripping her half-naked and defiling her body as she lay motionless and most likely dead on her sofa.

While at the house, the younger girl made a phone call over Facebook to a friend who heard her say: “Go on. Smash her head in. Bray her. F***ing kill her,” as the other girl laughed.

Wrightson suffered more than 100 injuries inflicted by weapons including a coffee table, television set, computer printer, a wooden stick studded with screws, a shovel and a kettle.

The attack began in the early evening at 9pm, until the girls stopped to take a selfie, in which they were smiling while bruised Angela was slumped on the sofa with bruises on her face.

The girls left the house for a “time out” at 11pm, to visit a friend. When he asked about their bloodied clothes, they told him they had both fallen over. They returned to Wrightson’s house at 2am, before calling the police at 4am to take them back to their separate care homes. The officers said they were in “high spirits”.

During the trial, shocking details emerged of how the girls’ lives spiralled into alcohol and violence. They began taking a cocktail of drink and drugs aged 11, frequently ran away from their care homes together and absconded from school.

A former neighbour said: “Separately they were all right, they could be quite sweet girls; but together they were devils.”

Girl A was described by her social services tutor as the most volatile young person she had come across.

The younger killer, known only as Girl B, used her smartphone to document the attack boasting to friends about it.

Both girls sobbed uncontrollably as they were convicted of murder on Tuesday.

The judge, Mr Justice Globe, rejected a challenge by the press to lift an order that gives the two girls anonymity. The order was challenged by the Times Newspapers, Daily Mail-owner Associated News, and Newsgroup, citing public interest.

However, objections were raised by Hartlepool borough council and Cleveland police over the welfare of the teenagers and the possibility of reprisals against their families. Wrightson’s family said the trial would haunt them for the rest of their lives.

Their statement said: “It’s true that Angela (or Angie as she was known to us all) led a troubled and at times chaotic lifestyle. And as a family we were not as close as we ought to have been. The chance to put that right has been taken away from us.

“Angie was attacked and brutally murdered in her own home, a place where we all have the right to feel safe. Listening to the details of her injuries and of her final moments has been a harrowing experience and something which will continue to haunt us each and every day.

“No sentence, regardless of its severity, will ever bring Angie back. The two girls responsible will one day be women themselves, free to live their lives and perhaps have children of their own. A right which was taken from Angie.

“If any positive can be taken from this experience it is the kindness displayed by those who knew Angie best. Angie’s infectious personality touched the hearts of so many people and it is those fond memories which we continue to cherish as we attempt to move forward.”