Lamara Bell, 25, who lay in a crashed car off the M9 near Stirling for three days, has died, her brother Martin Bell said.
Her partner John Yuill, 28, died in the accident. Police have apologised to their families for the delay in providing help.
Scotland's Justice Secretary Michael Matheson has now launched an urgent review into how the police handle emergency calls.
Police Scotland Chief Constable Sir Stephen House has apologised to the relatives of a couple who lay for three days in a crashed car, despite it being reported to police.
John Yuill, 28, died in the accident and Lamara Bell, 25, was seriously injured in the crash near Stirling.
Scottish police failed to react to a call over a fatal car crash because the information was not logged on their systems.
An investigation has been launched over fears a couple involved in a fatal road crash may have lain in their car for days.