An orange Suzuki Ignis, a blue Honda Civic and a white Peugeot Bipper were involved in the incident, which occurred about 3.50pm on Thursday, January, Sussex Police said.
Nicola Drummond, 44, of Long Furlong, Findon, sadly died following the three-vehicle crash, and a further five people were treated for injuries, the force added.
A spokesman said a number of people stopped to assist at the scene, including a man in his mid-20s who was riding a motorcycle and wearing a fluorescent jacket, and the driver of a white minibus.
The two individuals left the scene prior to police attendance and may have significant information which could assist the investigation, police added.
Officers are urging them, and anyone else who saw what happened, to report it online, call 101 or email [email protected] quoting Operation Lumley.