She is 22 years old, so it was obvious she could drive. The place where she tortured the newborn and where she lived were very close, and in the same town.
The road wasn't main street, but a back road that can be very dark. It just so happened that when she lit the baby on fire, another couple pulled up in their car and asked what she was doing.
Yes, a better "plan" (if we can call this evil that), would have been to truck herself and her newborn 1/2 mile into the nearby forest and murder the child there. Perhaps she couldn't be bothered with that?
Oh, I thought it was a main road. Hm. Well, I’ll be interested to see what more comes out of this story. Like, who was the father?