The victim's mother-in-law has also been booked for assisting her husband in the act, they said.
Khadia police said that in her complaint, the victim said that her father-in-law, Ambalal Patel had sexually assaulted her on February 2 under the pretext of applying oil on her legs, while her mother-in-law locked the room from outside.
According to police, the incident took place when the victim's husband was not at home.
Police said they were probing why the victim lodged a complaint in this regard only on Friday, almost after one and half months after the incident.
Medical report of the victim is awaited, police said adding that her clothes have been sent to Forensic Science Laboratory (FSL) for testing.
The accused duo has been booked under Section 376 (rape) and 114 (abettor present when offence is committed) of the Indian Penal Code (IPC). The duo have not been arrested, cops added.