Her family members and friends are still mourning her loss.
"I have nightmares after that," said Marquis Bevineau, a family friend.
"I spend time just sitting at home, not sleeping for two or three days. My health has deteriorated so much i can't work right now," Bevineau added.
Following the arrests of Barrett and two other men, Milwaukee Police Chief Ed Flynn said the shooters likely targeted the wrong house.
"Both defendants shot at this house from the front, at a time of day when any reasonable person would realize individuals were likely to be inside," the prosecutor said. "Even though the 'wrong house' was shot up, the intent was to shoot at a probably occupied residence."
"This young girl had no opportunity at life," said prosecutor Sara Beth Lewis. "It was taken from her. It was taken by Mr. Barrett."
Lewis said Barrett's actions showed no regard for human life. She added he maintains his innocence, but never showed any remorse for Petersen's death.
"My client has maintained his innocence in this case, but that doesn't mean he has no empathy for Laylah Petersen or her family," said Barrett's attorney Christopher Hartley
Barrett addressed Petersen's family before the sentencing came down.
"I'd just like to say how sorry I am for the family, for the loss of their daughter and their granddaughter," Barrett said.
"I know you all think I'm guilty, because of the verdict, which I don't agree with." Barrett said.
Judge Jeffrey Wagner told Barrett he was responsible for taking a sense of security away from Petersen's family and others in her neighborhood.
"The impact on the family, they're neighborhood, they are in shock as a result of your callous disregard, your impulsiveness, of shooting up that house and taking the life of this child who is certainly the most innocent victim this court has ever seen," Wagner said.
25-year old Paul Farr, who police said drove Barrett and a second shooter, Arlis Gordon, to the home was previously sentenced to five months in prison after pleading guilty to one count of aiding a felon.
Gordon, 24, pleaded guilty to second degree reckless homicide and three counts of recklessly endangering safety. He'll be sentenced December 8th.