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 father of a woman who was left severely hurt in a crashed car for three days after police reportedly ignored a 999 call broke down in tears as he told ITV News how he unknowingly drove past the spot on the morning of the accident.
Lamara Bell, aged 25, is no longer critical but remains in a serious condition in hospital after officers found her with the body of her boyfriend, 28-year-old John Yuill, who was killed in the smash.
Andrew Bell told ITV News that his daughter - herself a mother-of-one - was in a state of shock when she was found and thought she had been lying there just half an hour.
ITV News Scotland correspondent Debi Edward reports:
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.