A video of Gertrude -- she didn't give her last name -- has gone viral with more than 3 million views since it was posted online last Friday, a little more than a week ahead of the December 4 re-run vote.
"It's probably my last election," said the retiree from Vienna.
"There's not much future for me. But the young have all their lives ahead of them and it's up to them to see that they continue to do well. They can only do that if they vote wisely."
The left-leaning Alexander Van der Bellen, an independent candidate backed by the Green Party, posted the video on Facebook
at Gertrude's request. He is challenging Norbert Hofer of the far-right Freedom Party
in the election.
At the age of 16, Gertrude, her parents and two younger brothers were deported to Auschwitz, the German Nazi concentration camp in occupied Poland. Estimates vary, but about one million Jews are believed to have been executed at Auschwitz.
According to the video, Gertrude -- who says she is not religious -- was the only member of the family to survive.
'Shiver ran down my spine'
Gertrude says she is disturbed by the anti-migrant sentiment -- "the insult towards others. The denigration. The badmouthing" -- that she has heard during the campaign by the Freedom Party.
She reminds viewers of a comment made in October by the leader of the Freedom Party, Heinz-Christian Strache, who warned of possible civil war if the influx of migrants to the EU is not stopped.
"When Strache used the word 'civil war,' a cold shiver ran down my spine and I thought that shouldn't even be mentioned, not even be thought of," she says.
"I experienced a civil war as a seven-year-old and I've never forgotten it. It was the first time I saw dead bodies. Regrettably not the last.
"I've never forgotten it. It buried itself so deep in me that I'm still aware of it."
She did not specify what happened when she was seven, but the four-day February uprising
in Austria in 1934, also known as the Austrian civil war, marked the first mass European working class resistance to fascism. Clashes between socialists and fascists left hundreds dead.
Gertrude also recalled how the Nazis forced Jews to clean the streets of Vienna while people stood there and laughed. She says that today, there is again an impulse to "bring out the lowest in people" in Austria.
Rise of the right
Van der Bellen was elected the nation's first left-wing president since World War II in a vote in May, winning 50.3% of the vote. Hofer took 49.7%.
But the Freedom Party successfully challenged the outcome in Austria's high court, which found there had been irregularities in postal voting, and the election is being re-run on Sunday.
If Hofer wins, he will be the European Union's first far-right head of state.
His party has risen on a populist groundswell sweeping the continent, caused by the European Union's failure to make progress in the ongoing economic and migrant crises.
In a message posted by Van der Bellen on Facebook two days after the video, Gertrude said: "I am pleasantly surprised that the words of an old woman are being taken seriously.
"I want to thank Austrians for that. I am overwhelmed by this feedback."
CNN requested an interview with Gertrude, but a spokeswoman for Van der Bellen said she did not wish to speak further "due to security reasons."
Van der Bellen declined a request for comment, and representatives of the Freedom Party did not immediately respond.