The bridegroom's nephew fired from a gun from which one of the shots hit the bridegroom Dipak, 23, and he fell down from the horse.
The nine-year-old girl was admitted to BR Ambedkar hospital in Rohini where her condition was stable, said a senior police officer.
Vijaybhai Vaghasia, 32, his wife Rekha Vaghasia, 30, and son Veer Vaghasia, 4, died in the incident.
Based on a complaint received from the students, the police were looking into the issue, an official attached to the Amar Colony police station said.
The family members of the woman, a labourer, have alleged that she did not get proper health facilities which led to the tragedy
The Union Cabinet meet chaired by Prime Minister Narendra Modi also approved setting up of a National Financial Reporting Authority (NFRA) as an independent regulator for the auditors.