Ms. Mensah-Schramm said she reached a turning point in the early 1980s when she visited a concentration camp for the first time. When she came home, she vomited, but also resolved to make the same journey every year to commemorate the dead. She said that a few years later, in 1986, she was shocked to see a sticker at her bus stop that demanded the release of Rudolf Hess, the imprisoned Nazi war criminal. The sticker bothered her all day at work. When she came home that evening, it was still there. “No one had taken it off,” she said.

She used her keychain to scrape it away, and felt better. A few days later, she said she spent an entire night walking the streets of her comfortable Berlin neighborhood and was astounded by the scores of inconspicuous far-right messages she found. “After a few weeks, the stickers stopped coming back,” she said. “It shows the neo-Nazis that someone doesn’t agree with them.”

Ms. Mensah-Schramm’s activities do carry some risks. Over her 30 years of scraping, dissolving and painting over far-right slogans, she estimates she has been assaulted three or four times. But, she said, she has also been hugged by strangers and thanked.

Then there are the potential legal ramifications: “She’s walking a thin line, if you look at German laws regarding graffiti and property damage,” said Martin Gegenheimer, coordinator of a graffiti archive in Berlin. “She’s gotten in trouble a few times. But her position is that, morally, it’s more important to get rid of this stuff.”

As tensions rise over the refugee issue in Germany, others are following her lead. Last year, Ibo Omari, owner of a Berlin shop that sells graffiti paint and related items, founded an organization that has sponsored artists to convert some 20 swastikas into street art: Rubik’s Cubes, mosquitoes and owls. “She’s the grandmother of this project,” Mr. Omari, whose video of rehabilitated symbols has gone viral, said of Ms. Mensah-Schramm. “She’s way more experienced than we are. She’s not digitally connected like we are, but she should have been supported years ago.”

Still, thanks to workshops and classroom visits, Ms. Mensah-Schramm does reach young people. “She is taking responsibility for society,” said Julia Reidl, an English and geography teacher at the Goethe-Gymnasium in Karlsruhe. Ms. Reidl’s sixth, seventh and 11th graders have redrawn copies of real-life graffiti that says “I love Hitler” to offer more positive messages, like “I love cats,” in workshops with Ms. Mensah-Schramm. “They totally get into it,” said Ms. Reidl. “Some of the little ones said, ‘We want to go out and help you!’ It’s so important, especially nowadays, with all this hatred against refugees and Islam.”