The 30-year-old woman, who died on Oct 13, is the third fatality in the shooting, reports Bangkok Post.
In the Oct 3 incident, a 14-year-old boy opened fire with a modified blank gun in the luxury shopping mall in the centre of Bangkok.
The boy had bought the gun via a Facebook page, and on Oct 5 three men were arrested for supplying him the weapon and ammunition. Three other suspects were arrested the following day.
The teenager was brought to the Pathumwan police station for questioning but was in a confused state, saying he had heard voices telling him to shoot people, according to Gen Torsak Sukvimol, the national police chief.
He was admitted to a psychiatric hospital on Oct 6.
Two people were killed in the shooting – a female tourist from China and a female employee at the shopping mall from Myanmar – and five others injured.
One of the injured was Penpiwan Mitthampitak, 30. She was hit two times in the head and two times in the rib cage, and was admitted to the King Chulalongkorn Memorial Hospital for the.
Penpiwan died at about 2am on Friday (Oct 11), after ten days of treatment.
Maj Gen Nakharin Sukhonthawit, commander of the Metropolitan Police Division 6, said there would be no change in legal proceedings against the teen shooter because police investigators have already pressed premeditated murder charges against him.
The investigators would add updated details of the deaths and injuries to their probe report. They would include autopsy results of those who were killed in the shooting in the investigation report, added Maj Gen Nakharin.