I want to say to throw the book at her. I really REALLY do. But...
I also want to be realistic and and say that it's just as much a crime of misinformation and lack of resources as it is lazy parenting. LOTS of people don't buckle the car seat in. And sometimes they know better, and sometimes they don't. And sometimes they plain don't care. Yes, everyone SHOULD read the manual, but you know they don't. And frankly, I don't see how proper use can be a law when it's legal to sell used seats at consignment stores. If I buy a seat without a manual, what am I to do? I was broke in the first place, which is why I bought it used. I didn't know enough not to buy it used, because it was legal to do so. Or the punk at BRU told me how to put it in, when he had no clue. Or the cop pulled me over for speeding and never even mentioned it.
She was in the wrong, clearly. And SHOULD be charged with... something. Vehicular manslaughter, yes. But not in the same way as a drunk driver (inexcuseable) or serial speed offender (Nick Hogan). I am also a big fan of letting the punishment fit the crime... mandatory CPST certification and every saturday at free checks for a year would go a lot farther than just putting her in jail for a month.
I think the STATE should take notice in this as well. Laws need to be tougher, more enforced, more widely known, and the resources more readily available. Heck... if parallel parking (virtually non existent in all but the most urban areas) is a requirement for a DL, then a basic car and car seat safety class should be as well.