They had managed to persuade police officers to give them a lift home from the crime scene.
Miss Wrightson's mutilated body, which was naked from the waist down, was found on the sofa of her blood-spattered living room by her landlord who contacted police.
The alleged killers had developed an 'intense relationship' and became a 'bad influence' on each other after being taken into local authority care, Teesside Crown Court heard.
Weeks before the attack, one of the girls - who cannot be named for legal reasons - referred to her friend as a 'little partner in crime'.
The court heard how the pair, now 14 and 15, caused havoc by escaping from their respective homes at night, prompting police searches.
The girls befriended Miss Wrightson, a frail alcoholic, because she would buy alcohol for local teenagers in return for money for herself.
But after 'latching on' to Miss Wrightson and becoming regular visitors to her home in Hartlepool, the pair are accused of turning on her last December.
The alleged killers even defiled Miss Wrightson's body by placing gravel and broken glass around her private parts and ash in her right ear. As the attack continued, the younger defendant allegedly rang a friend who heard her yelling to her accomplice: 'Go on, smash her head in... f***ing kill her.'
A terrified Miss Wrightson pleaded for her life, the court heard. The younger attacker boasted about the incident to a friend, describing how the victim pleaded: 'Please don't. Stop. I'm scared.'
Jurors were told that the girls let themselves in through Miss Wrightson's unlocked front door at 7.30pm and left after 11pm, before returning in the early hours the next morning.
When another teenager confronted the pair after the alleged attack and enquired about the bloody clothes, they claimed they had fallen over.
Nicholas Campbell QC, prosecuting, said that after the murder, both girls knew police were looking for them because they had spent the night out.
Having failed to get hold of a taxi company or their carers - with one girl living with a foster family and the other in a local authority home - the girls turned to the police to get a lift home from the crime scene.
While in the vehicle the younger girl took a picture of the older accomplice before sharing it with friends on Snapchat.
It was accompanied by the caption: 'Me and (name) in the back of the bizzie [slang for police] van again.'
Mr Campbell told the court that the girls even called the police and complained about how long they had to wait to be picked up.
'After five minutes of waiting the older girl rang again and complained: "How long will you be? It's f***ing freezing".'
The girls sat listening intently in the dock as the chilling details of the case emerged. The day after the brutal attack, the older girl asked her carer how long a sentence for murder was.
Mr Campbell said Miss Wrightson was well known in the area as an alcoholic who could be 'difficult' and had been known to make hoax calls to the emergency services.
But he added: 'She was well liked when she was sober, she was a good neighbour, kept her house clean and tidy and would give chocolates to young children.'
The trial, which is likely to last more than a month, continues.
