Danica May Garcia was shot to death in her family's store by two men on motorcycles, CNN quoted the police as saying in Dagupan in Pangasinan province.
According to local officials, the suspected target was Danica's grandfather.
A community leader said that days before the shooting, the grandfather, Maximo Garcia, had turned himself in to police in an effort to clear his name, along with about a dozen accused drug users.
"We have a witness who came forward to identify the gunman," Dagupan police Chief Neil Miro told CNN.
"I will withhold the name of the suspect, but it seems it may have something to do with illegal drugs, too," the police chief said, adding "We are still investigating the real motive."
According to Human Rights Watch, since President Rodrigo Duterte launched the national war on drugs after assuming office on June 30, over 1,000 Filipinos have been killed by unidentified gunmen between July 1 and August 19.
More than 700 drug users and "pushers" have been killed in police operations, CNN added.
