The assailants overpowered the woman, Sudha Devi, and her daughter Gungun Kumari near Katoria bridge under Simultalla police station area and slit their throats with sharp object, the sources said.
The girl died on the spot, while her mother was wounded and referred to the Patna Medical College and Hospital (PMCH) in the state capital in view of her serious condition, they said.
The body has been sent for post-mortem, the sources said, adding a probe was on to find out the motive behind the attack on the mother-daughter duo, who hailed from Madhya Pradesh.