The incident happened yesterday, when the three sisters were travelling with their father and uncle in the Amritsar-Saharsa Jan Seva Express to Bihar, officials said.
The eldest of the three sisters, Albul, said their father and uncle were drinking alcohol and had a brawl, after which her uncle threw the sisters out of the train.
The deceased has been identified as Munni. The other two sisters -- Albul (12) and Saleema Khatoon (4) -- are in a critical condition and admitted at a hospital in Sitapur. The police are yet to trace their father and uncle.
While Munni was found dead at Ramaipur halt, around 11km from Biswan town in the district, Albul and Saleema were found injured at different places, police said.
The family belongs to Motihari in Bihar and the father and the uncle work in Punjab.
(With Inputs From PTI)