We'll have to disagree. imo, A mother IS responsible for ensuring her child's safety and that especially includes safety equipment in the family vehicles. Especially so if it is her "worst fear" that the child will die in that vehicle, as she has reportedly stated to police. This isn't about her husband's actions that day, it is about her actions and words.
Yes, the baby "could have fit" in the car seat....if was adjusted properly and it was not. That is a fact that came out in the hearing. I don't know of anyone who uses a child car seat improperly. In fact, when my twin grandchildren were born last year, at dismissal the hospital nurse examined their car seats and their installation prior to her allowing the children to be placed in the car.
JMO