If I were the mother of this child, the grandmother would never see my children again. The police said it best: there is "absolutely no excuse" for what she did.
Instead, I bet she is busy making excuses now, like, "I didn't know. It's not my fault. I didn't meeean to do it (but didn't try not to)." Or, perhaps, the kind of excuse I once heard from my child's grandmother, "It's your fault, because you didn't tell me not to."
Cutoff is what this woman deserves. Second chances are not an option for people who endanger children.