Angela Wrightson had more than 100 injuries on her body following her five-hour ordeal at the hands of the girls, who were 13 and 14 at the time.
The pair, who can not be named for legal reasons, were convicted of the murder of alcoholic Angela Wrightson by a jury at Leeds Crown Court.
The court heard that despite her demons, Wrightson was well liked in her community and would often give chocolates to young children and fed the local dogs.
The older girl said she struck Wrightson but only admitted to a charge of manslaughter. "Bray her. F***** kill her".
The court heard the defendants left the house for "time out" around 11pm, during which time they went to see a friend, covered in blood.
"The officer picked them up, their demeanour was fine, they were laughing and joking".
"Given the severity of their assault one would expect the girls to have shown a degree of remorse in the wake of her death", he said.
It was captioned: "Me and [girl's name] in the back on the bizzie van again".
Ms Wrightson was found naked from the waist down and grit and shards of glass had been scattered over her, jurors heard. Her living room was described as "akin to a bomb site".
Her violent outbursts signalled an "out of control" child with "a longstanding history of violence and aggression in whatever setting and from an early age", a mental health expert warned.
The older girl also took drugs, such as amphetamines, tramadol and codeine, from the same age and later began taking "blues", which she said made her "feel out of it, really bad". The jury took just over three hours to decide, the Daily Mail reports.
They were immediately led away from the dock.
The two girls will be sentenced on Thursday.
Police have also issued troubling images of the murder weapons used in the brutal attack on Ms Wrightson.
The younger girl said she felt lost without her mobile phone, which was described as her life, and they used it to document the events that followed.
On the day of the murder had attempted to visit her mother, but she had been heading out and had told her: "F*** off. Why don't you go kill yourself".
Detective Chief Superintendent Peter McPhillips, of Cleveland Police, said he had never come across a crime like it in his 25-year career.
Neighbour Alan Dixon said: "She was a kind, trusting, decent woman who was lovely when sober, but she was vulnerable in drink and she was taken advantage of by kids".
In a statement, Wrightson's family said: "No sentence, regardless of its severity, will ever bring Angie back".
A Serious Case Review into the case has been commissioned.