"She looked at me and said, 'If only had teeth down there,'" recalled Ehlers, who was a 20-year-old medical researcher at the time. "I promised her I'd do something to help people like her one day."
Forty years later, Rape-aXe was born.Ehlers is distributing the female condoms in the various South African cities where the World Cup soccer games are taking place.
The woman inserts the latex condom like a tampon. Jagged rows of teeth-like hooks line its inside and attach on a man's penis during penetration, Ehlers said.
Once it lodges, only a doctor can remove it -- a procedure Ehlers hopes will be done with authorities on standby to make an arrest.
"It hurts, he cannot pee and walk when it's on," she said. "If he tries to remove it, it will clasp even tighter... however, it doesn't break the skin, and there's no danger of fluid exposure."
Ehlers said she sold her house and car to launch the project, and she planned to distribute 30,000 free devices under supervision during the World Cup period.
"I consulted engineers, gynecologists and psychologists to help in the design and make sure it was safe," she said.
After the trial period, they'll be available for about $2 a piece. She hopes the women will report back to her.
"The ideal situation would be for a woman to wear this when she's going out on some kind of blind date ... or to an area she's not comfortable with," she said.
The mother of two daughters said she visited prisons and talked to convicted rapists to find out whether such a device would have made them rethink their actions.
Some said it would have, Ehlers said.
Critics say the female condom is not a long-term solution and makes women vulnerable to more violence from men trapped by the device.
It's also a form of "enslavement," said Victoria Kajja, a fellow for the Centers for Disease Control and Prevention in the east African country of Uganda. "The fears surrounding the victim, the act of wearing the condom in anticipation of being assaulted all represent enslavement that no woman should be subjected to."
Kajja said the device constantly reminds women of their vulnerability.
"It not only presents the victim with a false sense of security, but psychological trauma," she added. "It also does not help with the psychological problems that manifest after assaults."
However, its one advantage is it allows justice to be served, she said.
Various rights organizations that work in South Africa declined to comment, including Human Rights Watch and Care International.
South Africa has one of the highest rape rates in the world, Human Rights Watch says on its website. A 2009 report by the nation's Medical Research Council found that 28 percent of men surveyed had raped a woman or girl, with one in 20 saying they had raped in the past year, according to Human Rights Watch.
In most African countries, rape convictions are not common. Affected women don't get immediate access to medical care, and DNA tests to provide evidence are unaffordable.
"Women and girls who experience these violations are denied justice, factors that contribute to the normalization of rape and violence in South African society," Human Rights Watch says.
Women take drastic measures to prevent rape in South Africa, Ehlers said, with some wearing extra tight biker shorts and others inserting razor blades in their private parts.
Critics have accused her of developing a medieval device to fight rape.
"Yes, my device may be a medieval, but it's for a medieval deed that has been around for decades," she said. "I believe something's got to be done ... and this will make some men rethink before they assault a woman."
I dunno. This sounds like a really cool idea, but what about the rapes committed by someone the victim knows? They probably wouldn't anticipate the rape at all and so would not insert the condom. And what if a man that get bit by one of these became angry and took it out on the woman?