"I don't know what they're teaching about Nazis in school these days," Katie, whose grandmother is a Holocaust survivor, tweeted. "But here goes".
Holocaust denial, dragged up in the alt-right tidal wave crashing through the Western world, is alive and well in the highest office of the United States - just one reason why taking time to remember is so important.
Katie's grandmother was just two-years-old when Hitler invaded Poland in 1939, too young to understand that the world was changing around her.
When she was four years old, she saw that her three-year-old neighbour had been shot by Nazis.
Months later, she was separated from her family.
Katie's grandmother went to Majdanek concentration camp for being Polish.
She was 'adopted' by an officer.
But her 'adoptive parents' abandoned her when the Allies broke through to Poland.
She was found in one of the officer's homes days later, barely able to remember her own name.
Remarkably, the Red Cross reunited her with her family.