Brumfield was allegedly babysitting a 1-year-old in October when the child died after falling from a playpen.
Authorities in Ocoee, Florida, told Access that Brumfield, 29, was released on bond on Saturday.
According to the Orlando Sentinel, Brumfield claims the child died after sustaining a head injury from falling from its playpen – she reportedly did not call for help until two-and-a-half hours later.
However, the Ocoee medical examiners office reportedly ruled the death a homicide.
"It's not believable that a 1-year-old can balance themselves on a railing," a spokesman for the Ocoee Police Department told the newspaper. "We do believe her head hit a hard object [but] you would either have to fall harder or hit something with more force" than a 28-inch playpen fall.
Brumfield is the oldest of Thornton's four children, and his only child with his first wife, Melissa Gatlin.
"Mr. Thornton is estranged from Amanda and has had no contact with her for quite some time," a rep for the star told Access Hollywood on Sunday. "However, when informed about this situation, he commented that, 'Any time a baby's life is lost is an unimaginable tragedy and my heart goes out to the baby's family and loved ones.'"
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