Irene Walker, 27, is being held at the Adams County Jail on a $100,000 bond.
Sources told 9NEWS police were called to St. Anthony's North Hospital Sep. 17. They found an unresponsive 3-year-old girl with no visible trauma. She was later pronounced dead at the hospital.
A coroner report led police to believe she was murdered.
According to an arrest affidavit, the hospital staff advised police the child, Jersey Ruiz, was brought in by Walker and Ruiz's mother.
The affidavit says Ruiz was reportedly lethargic all day and vomiting before being brought to the hospital. She went to preschool earlier in the day, but her mom was called to pick her up.
According to the affidavit, when she was brought to hospital around 10 p.m. that night, she was not breathing and did not have a pulse.
Walker told police Jersey "fell down a lot" and "recalled a time when she (Jersey) broke her leg and never cried or complained and how tough she was," the affidavit read.
The Adams County Coroner told police Jersey's internal injuries were comparable to that of a "major car accident."
The coroner ruled her cause of death was "blunt trauma to the abdomen."
The affidavit says the child was treated at St. Anthony's Hospital at least three other times.
Walker is a stay-at-home mom who cares for her own two children. Walker is the sister-in-law to Ruiz's mother, according to the affidavit.
Walker is facing charges of child abuse resulting in death.