A Temple University Hospital spokeswoman said Keisha Williams, 34, died Thursday night at the hospital, where she had been listed in critical condition since the July 25 crash that killed Keiearra Williams, 15, Thomas Joseph Reed, 10, and Terrance Moore, 7, as they were selling fruit for a church fundraiser.
The children's funeral was held Monday. A family friend who was nearby and the woman who had been carjacked were also injured.
Prosecutors said Cornelius Crawford, 23, and Johnathan Rosa, 19, would face an additional murder charge each, totaling four counts of second-degree murder and conspiracy, as well as kidnapping, robbery, aggravated assault and sexual assault.
"My heart continues to break for the family and friends" of the victims, District Attorney Seth Williams said in a statement Friday. "I hope the knowledge that I am prosecuting these defendants to the fullest extent of the law will give the family some sense of justice during this time of unimaginable grief."
Authorities allege that they forced a real estate agent into her SUV as she left a house showing in north Philadelphia, then took off at high speed. About 15 minutes later and a mile away, authorities said, the vehicle went out of control at an intersection and plowed into the group on the corner.
Rosa's attorney, Christopher Warren, has said his client is cooperating with authorities and "can't get the image of the girl flying over the hood of the SUV out of his mind." Crawford had recently been released from prison after serving about five years for robbery. Warren said the two men had only known each other for a few days.