Ms Subasri was feeling very depressed in the past few days and hanged herself in her house on Wednesday night. Her parents took her to a hospital where she died today.
The girl's death comes days after 19-year-old Prateebha, daughter of a farmer, committed suicide for not passing the test.
Opposition parties led by DMK raised Prateebha's death in the ongoing assembly session while its leader MK Stalin urged chief ministers of other southern states and West Bengal to oppose the NEET, saying it discriminated against non-Hindi speaking students.
Police said Ms Subasri, who wanted to join an MBBS course, scored only 907 marks out of 1200 in the Class XII exam, but was hopeful of clearing the NEET as she had attended coaching classes.
Ms Subasri's father Kannan, a transport corporation employee, and mother had tried to pacify her and asked her not to worry and tried to divert her attention by taking her outside, including a temple.
This is the third suicide of a student over NEET in Tamil Nadu since last year. Anitha, a Dalit girl from Ariyalur, ended her life for failing to clear the NEET last year.
With inputs from PTI