Question: I'ma pretty smart person but I got so lost watching this film. Is she clairvoyant?
Question: If Sandra is at the scene of the accident, what is the purpose of the police officer showing up at the door to tell her Jim is dead?
Answer: Possibly she left the scene before the police arrived, so they did not know she had been there.
Answer: It's fairly obvious that this film's theme is that knowing the future changes it. I.e. knowing there would be an accident, she travelled there and caused an accident.