The incident happened shortly after 13.10 GMT on Friday, 17 March at The Pier on Pier Road in Walls.
The incident involved the 72-year-old woman, a black Citroen Berlingo and a parked orange Suzuki Swift.
The woman was taken to the Gilbert Bain Hospital in Lerwick and subsequently to the Queen Elizabeth University Hospital in Glasgow for treatment to serious injuries.
No one else was injured
Sergeant Calum MacAulay said: “Our enquiries are ongoing to establish the full circumstances of this collision.
“Officers from Highland and Islands Road Policing Unit will be attending the scene in Walls today (Saturday, 18 March) to carry out an investigation.
“We would urge anyone who may have information about the incident to contact 101, quoting reference 1585 of 17 March, 2023.”
