What does the part in song Jesus Take Wheel she cried when saw that baby backseat sleeping like a rock mean?

In the song "Jesus Take the Wheel," Carrie Underwood sings about a character who is driving when she sees an accident and thinks she is going to die. She cries out to Jesus for help, and He takes the wheel of the car and saves her. The part in question, "she cried when she saw that baby backseat sleeping like a rock," is meant to convey the intensity of the fear and desperation the woman feels in that moment. She is so afraid for her own life and the life of the baby that she is unable to control her emotions. The use of the phrase "sleeping like a rock" emphasizes the contrast between the woman's state of panic and the baby's peaceful sleep.