The image of Saffiyah Khan has been shared thousands of times since it was taken at Saturday's demonstration.
Ms Khan, from Birmingham, said she felt moved to intervene when she saw another woman surrounded by about 25 men.
"I don't like seeing people getting ganged up on in my town," she said.
Ms Khan, who said she was not part of an organised counter-protest, told the BBC she had been "quite surprised" when the photo was retweeted around the world.
She said she had initially been happy "to stay out of the way", but "stepped forward" when another woman shouted "Islamophobe" at members of the EDL who had gathered in Centenary Square.
"A group of 25 quite big-looking EDL lads, they surrounded her," she said.
"She was 360 surrounded... I stepped forward and identified myself as someone who supported her and contradicted them."
After that, Ms Khan said, protestors gathered around her instead, which led to the scene captured by a Press Association photographer.
Ms Khan, who was born in the UK and is half-Pakistani, half-Bosnian, said she "wasn't intimidated in the slightest".
She added: "He put his finger in my face. It was very aggressive. A police officer was there and the man took his finger out of my face. I wouldn't have responded violently."
The picture was shared by, among others, Piers Morgan, who called it "photo of the week", and Birmingham Labour MP Jess Phillips.
The BBC has been unable to reach the EDL for comment.

The fire swept through the secondary school dorm in Aladag in Adana province and authorities said it may have been caused by an electrical fault.
However, there were fears that the girls may have been unable to escape. The mayor said it was likely that a fire door had been locked.
The girls who died were aged 11 to 14.
The dormitory housed girls from impoverished families in nearby villages, reports said.
One of the girls who died was Zeliha Avci, 13. Her father was waiting on Wednesday for the authorities to allow him to collect her body for burial in her village.
"No-one has called me," Mustafa Avci complained. "We learned about the fire from the news and ran to the scene. Our children have been burnt to death and no-one gives us any information."
Mr Avci last saw his daughter at the weekend. "She was very keen to go to school and get educated, but her days are over now," he said.
Her old dorm, he explained, was torn down in 2015 and he was unhappy about the new one. "This was the only dorm in town. We didn't want to send her there, but we had no other option."
TV footage showed flames leaping from the roof of the building as firefighters battled to put it out.
Adana governor Mahmut Demirtas said some students had been injured when they jumped from windows to escape the fire. He said 34 students had been staying in the dorm and 22 were taken to hospital.
A government minister who visited the scene said claims that the fire exit had been locked would be investigated. Turkish authorities imposed a media blackout on local coverage of the disaster.
Anadolu news agency said the six people in custody included the head of the dormitory, three teachers and two other staff. They were being investigated on suspicion of causing death by negligence.
A viral photo of a woman smiling at an English Defence League (EDL) protester in Birmingham was snapped after she stepped in to defend a "fellow Brummie", she has told the BBC.
[NEXT_CONCEPT]
A dormitory manager and five others have been detained in southern Turkey after a fire claimed the lives of 11 schoolgirls and a teacher, reports say.