The incident took place in Chandera village late last night as the victim, identified as Soni Kumar, hanged herself from a mango tree hours after she failed in the board examination, the results of which were declared yesterday, Bahadurganj police station in-charge Vinod Kumar Singh said.
The body has been sent for post-mortem at Sadar hospital, he said.
The deceased was a student of Bahadurganj girls school, the officer said.