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.
The family of a couple who were left in a field for three days after a car crash have blasted police for allegedly failing to answer a 999 call.
John Yuill, 28, died and his girlfriend Lamara Bell, 25, remains critically injured after the smash near Stirling in Scotland on Sunday.
An investigation has been launched into the police failure to follow up on a report a Renault Clio had gone off the road.
Mr Yuill's father Gordon told the Daily Record newspaper: "It wouldn't have made any difference for John. His injuries were such that he died on impact.
"But I feel it may have made a difference for Lamara. My heart goes out to her family for that."
Police Scotland told ITV News it would be inappropriate to comment at this time as an investigation is ongoing.
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.