Susan Norman, 68, died when tonnes of mud and rubble engulfed her flat in Looe, Cornwall, in March 2013.
An inquest jury concluded Cornwall Council had not listened to "consistent and frustrated complaints" from residents about previous landslips.
The authority has apologised to Mrs Norman's family.
More on the landslide inquest and other news from Devon and Cornwall
The court heard neighbours had warned Cornwall Council about the risk of erosion and questioned the stability of the land years before the fatal accident.
Mrs Norman's landlady, Christina Miller, told the inquest as soon as her tenant raised concerns she had called in a structural engineer who warned about the risk of "catastrophic collapse".
A post-mortem report read to the jury at Truro Magistrates' Court said Mrs Norman died immediately.
The jury said in its findings: "Cornwall Council did not listen to regular consistent and frustrated complaints by the residents. Cornwall Council did not respond to an independent report highlighting risk."
It added: "The landslide was caused, or more than normally contributed to, by a failure of Cornwall Council to prevent the surface water moving from St Martin's Road on to the rear of Veronica's (Mrs Norman's house)."
After the inquest, Mrs Norman's daughter Helen Hazeltine said: "She was taken away from us and she didn't have to be.
"This should never happen again and I don't want anyone else to go through this, at all, ever."
Kate Kennally, Cornwall Council's chief executive, said: "I would like to apologise to Mrs Norman's family and friends and express our sincere condolences for their loss."
She said it would "not be appropriate to comment in more detail", as court proceedings against the council and its civil engineering arm CORMAC had been lodged.

The strikes will affect hundreds of thousands of people who use the Southern Rail network in England every day.
But many commuters say strikes are just part of the ongoing daily disruption to Southern's service that is having a huge impact on the way they live.
Businesses are suffering and some workers have had to stay at home, while others have tried to find alternative routes into work, they say.
Frustrated by the continuing disruption, three passengers and a cafe owner agreed to video blog their mornings.
50-mile cycle ride again
John Holah, 36, is from Earlswood, Surrey. He works as a web developer in east London. John says it's not just on strike days that it's quicker to cycle the 50-mile (80km) round trip to work.
Cafe 'losing business'
Debbie Davis, 54, runs Beryl and Pegs Coffee, Tea and Sandwich Bar opposite Reigate station. Debbie says her cafe has been empty all morning.
Bus from Gatwick
Alison Braganza, 39, normally travels from Ifield, West Sussex, to central London. She's just started a new job and has been repeatedly late during her probation period.
Flying to meeting
Mark, 52, is an asset management consultant and had a meeting in Scotland. He couldn't catch a train into London so his company had to change its policy to allow him to fly to Glasgow.
Production by Dan Curtis and Ed Ram.

The Highlands and Islands have been enjoying a lengthy spell of fine, sunny weather.
Michael MacDonald, of Invergordon RNLI, captured the calm conditions and sunset on Monday during a training session for the crew.
The training in the Cromarty Firth took the volunteer crew close to a number of North Sea oil and gas rigs and platforms anchored in the firth.
A council ought to have known a grandmother faced "a real and immediate risk of death" from landslides, jurors have said.
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Rail passengers have faced more travel chaos as striking train drivers hold the first of six, day-long stoppages planned for this month.
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