The hitchhiker can be seen as a zombie before she is actually killed, reconstructed and brought back to life. This is because the abandoned house scene - where she is clearly visible as one of the dead townfolk - was originally placed in the film after her resurrection.
When the young female hitchhiker is taken from the truck, she is thrown onto the muddy ground. Her face is covered in mud, before the rock is smashed onto her face. Later when we see the videos of Dobb's "murders and creations" the young female hitchhiker is being held down on the hood of the truck, and her face is clean before they smash the rock down on her face.