Amy Lorenzo, 12, and her sister Marlene, 14, were walking to school in a crosswalk on April 4 when they were both struck by a truck.
Marlene died that day, but Amy was hospitalized in critical condition and in a medically induced coma.
On Monday, police announced that Amy had died.
"It's with deep regret and a heavy heart to announce that Amy Lorenzo died earlier today," LAPD Det. Moses Castillo wrote on Twitter. "Keep her family in your thoughts & prayers. Family has asked for privacy and is very appreciative of the out pouring of community love & support."
Investigators were trying to determine if the driver was distracted at the time of the collision. The driver was not arrested.