DNA Tests have finally shown nurse Lisa Jane Browne, 27, suffered a rare condition which could have caused her heart to stop in shock when the alarm woke her in January 1998.
A coroner recorded an open verdict saying the cause of Lisa's death was a mystery.
But now Lisa's mum wants the inquest re-opened after discovering Lisa had Long QT Syndrome.
Doreen Harley and her husband Terry - who have spent the past seven years trying to prove their daughter was ill - had a sample of Lisa's tissue sent to Sweden for analysis two years ago.
She said: "It took 20 months to diagnose Lisa definitely had Long QT. We could never accept she died for no reason. To put everything in place we need a certificate showing the new cause of death."
The syndrome, which affects around one in 7,000, is a disorder of the heart's electrical rhythm - leaving victims open to heart attacks which can be produced by sudden shocks.
Mrs Harley, of Connah's Quay, North Wales, is convinced the alarm stopped Lisa's heart.
The family then found Lisa's sister Rachel had Long QT. She had a pacemaker fitted, which saved her when a shock triggered a heart attack.
Cheshire coroner Nicholas Rheinberger is considering reopening Lisa's inquest.