She was Tantima Thavorn, 37, mother of a young girl.
She becomes the second Phuket fatality in the Seven Days of Danger national road safety campaign that began at 00.01 on Tuesday.
Khun Tatima's death occurred at Vachira Phuket Hospital despite the efforts of doctors and nurses.
Police investigators are still trying to determine what happened when her Ford Fiesta collided with the tour bus on Phuket's west coast road between Patong and Kamala on Tuesday.
Most of the 30-plus Russians on the bus required hospital treatment after the bus toppled off the roadway and landed on its roof. But none were admitted for care.
Eighteen people - 12 men and six women - have been admitted to Phuket hospitals in the first two days since the Seven Days of Danger campaign began.
Today was the third day. An update to the toll is expected tomorrow.