They would like to speak to the occupants of what is thought to be a Ford vehicle, which was travelling along the A641 Huddersfield Road at about 8.30pm on February 24.
Police said it was overtaken by the silver Vauxhall Astra which was involved in the collision a short time later.
Jane Floweth, who was 68 and from Ilkley, was a passenger in a blue Honda Jazz which was in collision with the Astra on Common Lane, near the Guide Post Hotel.
She was taken to hospital where she later died from her injuries.
A 24-year-old man has been arrested on suspicion of causing death by dangerous driving and remains on bail pending further enquiries.
Anyone who can assist the investigation is asked to contact the Major Collision Enquiry Team on 101, quoting crime reference 13180092933.