Two teenagers who were in care and described as being out of control have been sentenced to life in custody for torturing a vulnerable woman to death in a “cowardly attack” that lasted more than nine hours.

Angela Wrightson, an alcoholic who craved company and regularly invited strangers into her home in the hope of conversation, was murdered last year by the two girls in her own living room.

She would often sit on the doorstep of her Hartlepool home talking to passersby. A court heard that she had allowed children to drink and smoke in her home, making her a popular figure among some in the area.

On 8 December, 2014, on one such occasion, two girls aged 13 and 14 visited her home and demanded she buy them alcohol. Wrightson considered the two girls friends, the court heard, and she obliged. In the hours that followed, the 39-year-old suffered more than 100 injuries. The teenagers turned on her, launching a sustained attack using a television set, coffee table and wooden stick to torture and eventually kill their host.

The pair – who cannot be named because of their age – were found guilty of her murder earlier this week after an eight-week trial. On Thursday as the judge gave them life sentences, ruling that they should be detained for a minimum of 15 years, sobbing was heard from their families in the public gallery.

Sentencing the girls, Mr Justice Globe said: “Children, such as you, were attracted by her generosity and took advantage of her. You would go to her home. She would agree to buy you alcohol and cigarettes. She would let you drink and smoke in her home.

“On occasions, when it was obvious that she was being pestered, neighbours did what they could to scatter those who were congregating at her home. Nobody, though, expected her to come to any harm, still less to be attacked in the manner you killed her.”

A few weeks before Christmas in 2014 Wrightson was made to plead for her life as the girls forcibly restrained her, only stopping the assault to pose for pictures, which the younger girl – said to be obsessed with her phone – sent to friends on 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 using them as a “taxi service”; again they took a picture and shared it on Snapchat.

Globe said: “It was an attack that was carried out by the two of you as a pair. This made it a cowardly attack. It was an attack carried out in Angie’s own home. She kindly invited you in; she kindly went out to buy you what you wanted; she kindly let you stay. You then abused her hospitality and attacked her again and again in the very place where a person is supposed to feel safe.

“It was an attack that included gratuitous degradation: you took photographs in the room when she was injured; you published one of them; you smashed up her home … You then left her alone not knowing or caring if she was alive or dead.”

The judge spoke of an emotional letter he had received from Wrightson’s mother that described her horror at seeing her daughter’s battered body in the mortuary. “She does not think she will ever be able to blink those images away,” Globe said. “She cannot understand how you could have been as violent as you were. She is not alone in that view.

“She has been disgusted by the laughing and giggling and sharing of photographs during the time of and immediately after the attack. She eventually found it so difficult to listen to the detail of the evidence that she had to stop coming to court.”

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

In rejecting the application the judge revealed that the older girl had tried to kill herself four times during the course of the trial. He said some of these attempts had happened on court premises during the trial and said one court official had saved the girl’s life when she had tried to strangle herself with her own hair in the toilet.

The teenager, known only as Girl A, who suffers from a mental disorder is currently on “two-minute visual checks” as she is considered a high-risk suicide risk.

The judge told the older girl: “I have seen you harming yourself. You scratch away at your features. You bang your head against walls. You do everything you can to harm yourself. Those looking after you are on high alert to look after your safety. I am prepared to take notice of your current state of health as a mitigating feature. It is also highly influential in my decision as to anonymity.” He said the younger girl had also self-harmed during the trial.

Both girls denied 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. But the judge said they acted in tandem.

“This was a sustained attack over a long period of time carried out with weapons in many different ways. She undoubtedly suffered considerably, both mentally and physically, before she ultimately lost consciousness and died. Her alcoholic state, considerable though it was, may have numbed the pain but I stress the word may, and it most certainly would not have taken it away.”

It emerged that 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 said the violence inflicted against Wrightson was “born out of childhood stupidity” and the girls were “clearly out of control”. He argued that the girl 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 the pair turned on her during an argument.

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 71 injuries to her face and 31 to her body 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 afterwards.

Both girls sobbed uncontrollably as they were convicted of murder on Tuesday but showed little emotion during the sentencing. The judge told the girls they would have been facing much longer sentences if they were adults.

The judge said the starting point for his consideration of their minimum sentences was 12 years, due to their age. But he said he had increased this due to the aggravating factors in the case.

Wrightson’s family said the trial would haunt them for the rest of their lives as they were told that she pleaded for her life before being murdered. 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.