The baby girl was kidnapped from a slum area in suburban Kandivali in the wee hours of Monday, said senior Inspector of Kandivali Police Station Mukund Pawar.
After going through CCTV footage of the area it was found a woman in her mid 30s, later identified as Aarti Jagdish Patel, had lifted the baby, he said.
Aarti and the infant's mother were not on good terms. Hence, to teach her a lesson, Aarti came up with a plan to kidnap her daughter, Pawar said.
The accused were booked under IPC sections related to kidnapping, he added.