Gamara Mosley, who turned herself in Wednesday morning, is also charged with criminal conspiracy.
Mosley's lawyer said he'll be making a push for pre-trial house arrest, and for his client to be tried within the juvenile justice system.
Richard Jones, 14, also turned himself in to police alongside his attorney on Monday in connection with the attack. Jones is charged with murder and criminal conspiracy.
A 13-year-old girl and a 10-year-old also spoke with police, but are not facing charges.
Mosley, Jones and others were allegedly involved in the June 24 attack on the 2100 block of Cecil B. Moore Avenue in North Philadelphia.
[Ads /]
RELATED: Officer creates portrait of 73-year-old man killed in North Philly attack
Police said 73-year-old James Lambert, affectionately known as "Simmie," was attacked by a group of young males and females.
Police said the suspects struck Lambert several times with objects, knocking him to the ground.
In surveillance video released by police, the suspects can be seen attacking the victim with a traffic cone.
[Ads /]
Police said Lambert suffered injuries to his head and later died. The medical examiner said Lambert died from blunt force trauma.
The District Attorney's Office released a statement Wednesday saying, "A 14-year-old boy and 14-year-old girl have been charged with Third Degree Murder and Conspiracy. No one else in connection to this crime has been charged at this time. DA Krasner and everyone at the DAO express our deepest condolences to Mr. Lambert's family, friends, and community regarding his shocking and tragic death."
Anyone with information is asked to contact the Philadelphia Police Department Homicide Unit at 215-686-3334/3335.