Absent the knowledge of whether she was driving the car "safely" (as you choose to define it), was this the action that would be taken by a reasonably prudent individual?
Actual reckless, careless operation of a vehicle in the public way, or just more nanny-statism?
The former. She was GAMBLING her baby's life on everyone else not making a mistake. If it were just her life, I'd be inclined to let it go. But
Wait that's not enough ... the child might wave his/her arms or grimace or otherwise create a visual distraction to the driver.
We need an opaque, soundproof enclosure for children in cars.
Wait! That's still not enough. The child might dirty his diaper or throw up, or something that creates a bad smell that distracts the driver.
We need an airtight, opaque, soundprooof box for the child in the car.
Face it, otherwise a child in the car is just unsafe.