An Occupy Wall Street activist is due to go on trial in New York on Monday, almost two years after she allegedly assaulted a police officer.

Cecily McMillan, 25, faces up to seven years in jail after being charged with assault in the second degree, a Class D felony in New York. Police allege that McMillan elbowed an officer in the head during a protest in lower Manhattan in March 2012.

McMillan’s attorney, Martin Stolar, told the Guardian that while there was “no question” the officer was struck below the eye by McMillan’s elbow, he planned to argue that no crime had been committed.

“The question for the jury is whether she intentionally assaulted him,” Stolar said. “We’re going to present evidence that indicates: No1 that she had no idea it was a police officer behind her and No2 that she reacted when someone grabbed her right breast.”

Stolar said it was being grabbed from behind that prompted McMillan to throw the elbow.

“That does not constitute a crime. That constitutes a bit of over-policing and an accident as a result of that.”

Protesters gathered at Zuccotti Park on 17 March 2012, to mark six months since the start of the Occupy protests. More than 70 people were arrested as demonstrators attempted to “reclaim” the space, which had served as a hub for Occupy Wall Street until the encampment was evicted in November 2011.

Although McMillan was active in Occupy Wall Street, Stolar said she was not part of the demonstration on 17 March.

“On that particular night she happened to be meeting friends,” he said. “By the time she got down [to Zuccotti Park] to meet her friends the police had decided to clear the park, so she was getting out of the park just like she had ordered everybody else to do.”

McMillan, a student at the New School and a union organiser, has declined to discuss the case while it is ongoing. At the time of the incident, reports suggested she was handled roughly during her arrest. In the days following she told the media she had suffered bruising and had been hospitalised.

“I am innocent of any wrongdoing, and confident I will be vindicated,” McMillan said in a statement in March 2012. She said she had a “long-standing personal commitment to non-violence”.

“She’s very upset about the fact she’s been living behind the eight-ball on this for two years,” Stolar said. “It’s anxiety of living under the cloud of being falsely accused and looking at the prospect of seven years in jail. That doesn’t make anybody happy.”

The case was due to begin on Thursday 6 February, but was postponed while a judge was appointed. Jury selection is due to begin on Monday.