Chen was accused of taking part in a riot on August 31, 2019, when protesters used debris to set up roadblocks in Wan Chai and clashed with police.
In 2020, a District Court judge acquitted her and ruled that she had no case to answer, before the Department of Justice lodged an appeal.
The Court of Appeal later ordered a retrial of four defendants, including Chen. She was the only one out of the four to not plead guilty in the retrial.
In sentencing, Deputy District Judge May Chung noted the case was very serious.
But the judge decided on a reduced jail term, after noting Chen was first brought to court for rioting five years ago.
Three others in the case each received a jail term of two years and five months after pleading guilty.