"I thought I was going to die," she said. "I thought he was going to kill me. I had it in my mind that I was going to be shot."
WATCH: Video shows altercation between CPD officer, Black woman walking dog
COPA is investigating the Aug. 28 incident. It began when the officer ordered her to leave the beach, which was closed.
"I know that as soon as he got out the car, I'm thinking to myself, how can I kind of deter the situation? How can I deescalate the situation?" she recalled.
RELATED: COPA investigating altercation between Chicago police officer, Black woman walking dog
Cell phone video caught some of what the two said to each other. There is a beep as the officer, who is not wearing a mask, turns on his body camera.
"Now understand this," he begins.
"Please don't," Brown interrupts. "Please respect my space. It's COVID. Six feet."
"Respect your space? I'm about to put handcuffs on you," the officer replies.
"You don't have a mask on!" Brown objects.
"I don't need a mask! I'm outside!" the officer retorts.
"I'm clearly walking away," Brown told Good Morning America. "This man is getting out of this car. He's saying that he's going to take me to jail and I'm never going to see my dog again. This is ridiculous."
Last week, Chicago Police Superintendent David Brown followed COPA's recommendation and placed the officer on administrative duties, pending COPA's inquiry.
"It's, uh, concerning what we saw on the video, but I want to make sure that COPA moves this to the top of the priority list and gets this done," Mayor Lori Lightfoot said at the time.
Nikkita Brown said at the time that other people were walking out on the beach at the same time, and felt she was targeted because of her race.
It's unclear if COPA has interviewed Nikkita Brown. The agency said it has reviewed the officer's body-worn camera video as part of its investigation.
You can watch the full interview on Good Morning America Thursday morning.