"We didn't even do anything wrong and they pepper-sprayed us, 20 of us down at the station," she said. "I am [in a lot of pain] - my face hurts."
Up to 100 protesters in the station were hit with pepper spray, after the main march in Sydney dispersed.
NSW Police have confirmed three people were arrested in Sydney earlier this afternoon, all before the rally officially began.
Assistant Commissioner Mick Willing said there was "minimal disruption" at events in Sydney, Newcastle, Byron Bay, Lismore, Coffs Harbour, Port Macquarie, Wyong, Wagga Wagga and Broken Hill, which were "essentially peaceful".
"Initially, we had a tough job in Sydney as the police operation was already underway when the Supreme Court decision was overturned, but we rapidly changed plans to ensure the event would run smoothly," Assistant Commissioner Willing said.
Police said a 23-year-old man and 15-year-old boy were involved in a "physical altercation" at Town Hall station at about 2.20pm, on their way to the protest, so they were arrested.
The older man was tasered after he allegedly became aggressive towards officers, police said. He was taken to hospital and is expected to be charged with affray, while the teenager was cautioned.
A 51-year-old man was arrested at about 2.30pm for an alleged breach of the peace, however he was released and no further action is expected to be taken.
"Some 20,000 protesters turned out in Sydney today, and to only have three arrested is a really positive result,” Assistant Commissioner Willing said.
According to witnesses and video footage, additional arrests were carried out following the rally when most of the demonstrators had dispersed.