This stood out to me:
"Nobody expected this," Small said in an interview at the courthouse. "I know she gets violent, but never thought she would do this to her baby."
And also that the boy was autistic or had leanings of such. If that was so, then violent tendencies and dealing with an autistic toddler do not mix. A normal toddler can exasperate even the most patient of parents, an autistic child even more so. I wouldn't be surprised to find out that she killed him via shaking, hitting, etc.