The woman allegedly owned an illegal gas-refilling shop in the building where the fire broke out after a short-circuit, which was followed by massive cooking gas cylinder explosions, a senior police official said.
Police are awaiting a forensic report and the woman is likely to be arrested.
A case on charges of negligent conduct with respect to fire or combustible matter, causing grievous hurt by act endangering life or personal safety of others and negligence causing death was registered in connection with the incident, the official said.
A woman and her two minor daughters were charred to death in the incident and around 23 people injured. Mithilesh (38), another resident of the building, and Nikhil (16), a passerby who was returning home from a gym in the locality, later succummed to their wounds in hospital.
Three persons were killed and 11 injured in another fire incident reported around half an hour ago in east Delhi's Gandhi Nagar area on the same evening.