Lorraine Thorpe, now 16, of Clapgate Lane in Ipswich, was found guilty in August of murdering her father Desmond Thorpe and a woman called Rosalyn Hunt.
Thorpe, 15 when the murders took place in 2009, was told at the Old Bailey she would serve at least 14 years.
Paul Clarke, 41, also convicted of two murders at Ipswich Crown Court, was sentenced at an earlier hearing.
Clarke, of Mountbatten Court, was also jailed for life and told he must serve a minimum of 27 years.
Far from being sorry, Lorraine appears to have gloried in it, describing to her friends at one stage how she stamped on Rosalyn's head”
Mr Justice Saunders said Thorpe could be "manipulative" and was not acting entirely under Clarke's control, adding: "She found violence funny and entertaining."
The bodies of Ms Hunt and Mr Thorpe were found at separate addresses in Ipswich in August 2009.
Both Clarke and Thorpe had denied the charges and gave no evidence during their trial.
They had repeatedly beaten and tortured Ms Hunt and then smothered Mr Thorpe to death.
The judge said: "Far from being sorry, Lorraine appears to have gloried in it, describing to her friends at one stage how she stamped on Rosalyn's head."
Paul Clarke Paul Clarke had denied the charges and gave no evidence during his trial
He said the only "possible explanation" for her father's murder was "the fear that he would go and tell the police what happened to Rosalyn Hunt".
Mr Justice Saunders described the case as "exceptional" and the story of Thorpe "appalling".
The court heard Thorpe and her father lived in "squalid" flats and sometimes even in tents.
"She was spending all her time with middle-aged alcoholics to whom violence had become normal," the judge said.
"It had become part of their way of life. The alcoholics fought with each other.
"They stole in order to get the drink they craved."
Social services could not keep track of her and when she was placed in a school she went back to her father, the judge told the court.
Through drinking the Thorpes met Clarke and lived at his flat for a time.
"She has been left with no real understanding of what is right and what is wrong," Mr Justice Saunders said.
"To describe her upbringing as not being a proper upbringing would be an understatement but it has left her as a violent young woman and a highly manipulative young woman as well."
Graham Parkins QC, defending, said: "It was highly inappropriate for this young girl to be playing a role of carer to her drunken and indeed very frail father.
"She never really had much of a chance in life."
Britain's youngest female killer, Mary Bell, was held at the age of 11 in 1968 for the manslaughter of two boys aged three and four.