Aliesha Sams, 22, was arrested in connection with the death of her 9-month-old son, Jaden Sanders.
According to an arrest affidavit, Sams was arrested Wednesday despite the child's death on July 6.
Investigators said Sams told police she noticed injuries on her son after she left him alone with her boyfriend, Anthony Arista, but never sought medical attention.
Sanders died shortly after paramedics and police were called to the Rodeway Inn on Austin Highway where Sams and Sanders were living with Arista.
The child had what appeared to be a cigarette burn on his back and blood in his mouth, the affidavit stated.
The Bexar County medical examiner determined Sanders was abused and ruled the cause of death as head trauma, the affidavit stated.
Arista was named as a suspect, and the affidavit stated Sams admitted to police she knew Arista had a violent temper, and suspected he had beaten the baby.
Sams was charged with causing serious bodily injury to her infant.