The trio opened fire at district vice president of Samajwadi Yuvjan Sabha, Shanky Rastogi, when he was at his medical store, police said.
Two of the bullets hit Toshi Rastogi, who was standing nearby, on her head and chest, killing her on-the-spot, they said.
Out of the three assailants, two have been arrested, they said, adding, police personnel have been deployed at the spot following the incident.
It was not immediately known whether Shanky and Toshi were related to each other, they said.
