If what she states is true... why in the world would she babysit the infant if she had a toddler that (supposedly) treated him like that? IF this is true she's still guilty in my mind because this could have been prevented by not staying overnight knowing her toddler had these sorts of issues.
Taken from your article:
On October 25, she was watching the boy along with her own 3-year-old daughter, and told police she got up in the middle of the night to use the restroom and found the boy unresponsive. Her daugther was “in the bedroom hiding in a corner,” she said, adding that she believed the girl had beaten the boy with a jar of petroleum jelly.
The complaint said that Flint claimed to have seen her daughter hit, scratch and bite the boy in order to get attention. She claimed she had to be careful with the girl around the baby because of her anger and “undiagnosed neurological disorders.”