In 1973, a military group led by dictator Augusto Pinochet overthrew former president Salvador Allende and killed him.
During Pinochet's regime, "more than 3,200 people were executed or disappeared, and scores of thousands more were detained and tortured or exiled," The New York Times reports.
The Association of Relatives of Detained and Disappeared of Chile organized the march to protest Pinochet's rule and honor the people who died during his regime.
Mancilla told the Chilean website, La Tercera, when police began making arrests, the woman stood strong.
"She reacted and stood before the policeman with a defiant look," he said.
However, the image of the unidentified woman has caused controversy.
Some people are denouncing the praise she's been receiving.
Translation of Hector Cheix's comment: "And that face of hatred on a young girl who does not even know what she is doing there."
In the comments section of Buzzfeed's article, people did some digging and found the bottom picture of the same woman giving the middle finger to the policeman.
Meanwhile others are applauding her act of bravery.
Whatever your stance is on the picture, it's so powerful that it ignited a fire, and conversation, between people around the world.
And that's what matters.