Prabhawati Gogia was killed in Sector 4 when she was alone.
Shambhu, 35, and Gaurav, 19, residents of Khelgaon in Delhi's Hauz Khas along with Lucky, 40, were nabbed. Most of the looted jewellery was recovered from them.
The three were arrested while they were planning to board a train for West Bengal from where they hail.
Three more people, involved in the robbery and murder, are yet to be arrested.
Lucky, living in sector 9 here, worked as a domestic help at several houses in sectors 4 and 7, said police.
Lucky planned the robbery with her relatives. She told the others that there were three cars in the house and they would know the elderly woman was alone if they did not see any vehicle.
A CCTV camera footage has captured suspicious movement of a woman (Lucky) near Gogia's house around the time the crime took place Monday.
The widow lived with her son, daughter-in-law and two daughters.
The murder came to light when daughter-in-law Kalpana, a school teacher, returned home after 2 p.m.