The incident took place around 8.30 am.
Shobha Rani was taking her two daughters to school when the truck hit her scooter from behind, police said.
All three fell on the road, said an official attached to the Uppal police station.
A passer-by took them to a nearby hospital where the doctors declared the younger of two girls, a class III student, as dead on arrival.
The mother and the elder daughter were undergoing treatment, the official said.
Meanwhile, reacting to reports that potholes on the road caused the accident, Hyderabad municipal commissioner B Janardhan Reddy said the road was "perfectly motorable".