Officers found the corpse under a blanket on a bed after ignoring the 51-year-old niece's claim that her aunt was sleeping and should not be disturbed, a police statement said.
A preliminary inquiry had determined that the niece, who was taken to a psychiatric hospital for examination, may have covered up the death for financial reasons, it added.
Austrian news agency APA quoted police investigator Gerald Hoebart as saying possible theft was being looked into since the younger woman appeared to have lived off her aunt's pension since the death and used her cashpoint card to withdraw money.
An autopsy was planned to check whether any foul play was involved in the death, believed to have happened in August 2006.
Ref: Reuters