On Jan 17, officers responded to a call of a child not breathing shortly after 7 a.m. in the 4600 block of Bandera Street.
The young girl was airlifted to a local trauma center due to a head injury, but she succumbed to her injuries and died the next morning, police said.
After an extensive investigation, the Montclair Police Department obtained an arrest warrant for Alma Gonzalez, who was the girlfriend of the victim's father.
Gonzalez was arrested Jan. 30 at a home in an unincorporated area of San Bernardino County for assault on a child causing death. She was then booked at the West Valley Detention Center.
Additional details on the incident were not released.