Molly McNamara was one of the ghosts haunting Highway 41. She was however unaware of her death, and continued to look for her husband every year.
Background
On February 22, 1992 Molly McNamara and her husband David McNamara were driving along Highway 41 in Nevada when they hit and killed Jonah Greely. Molly died, but was unaware that she had died in the accident. Each year on the anniversary of her death, car accidents occurred on that highway caused by Jonah Greely chasing Molly into the road.
When Sam and Dean met Molly, they did not tell her that she was dead, hoping she would help them find Jonah's remains. They found Greely's cabin, but Jonah grabbed Molly and started to torture her. Greely was dispatched when Sam salted and burned his corpse.
Supernatural animated Molly McNamara
Finally the boys revealed to Molly that her husband was alive and she was dead. At last she accepted this and her spirit disappeared with the sunrise after she decided to move on.
Trivia
- In the novel Supernatural: Bone Key, Bobby Singer explained that the reason Greely and Molly were corporeal was all of the spiritual energy surrounding them was concentrated into that one night.