The bit about the culvert was incorrect. Someone must have been confusing her for Orange Socks, who was in a culvert.
I verified this with Detective Bean. He says that the exact spot where she was found is unknown because the topography and foliage has changed significantly since 1980. She was fairly close to highway, but the highway was only one lane in each direction in 1980. It has been widened to two lanes in each direction, so the spot where she was found is likely now covered by the pavement of the right-hand northbound lane.
He says his crime scene photos show no culvert, or any other landmarks that can reference her exact location to the highway as it appears today.