Jockey Nikita McLean has successfully argued that a five-month suspension for assaulting her sister and fellow rider Jackie Beriman was "manifestly excessive".

McLean's lawyer Patrick Wheelahan told the Racing Appeals and Disciplinary (RAD) Board the suspension would equate to $70,000 in lost income.

RAD Board chairman Judge Russell Lewis, allowed the appeal, reducing the severity of the original sentence to two-and-a-half months.

McLean, who originally pleaded guilty to punching her sister in the face outside the jockeys' room at Hamilton on April 14, can now resume riding on June 30.

The Board heard the assault occurred as part of a marital row in which Beriman conducted an affair with her sister's husband, jumps jockey Brad McLean.

Judge Lewis said the case involved betrayal by McLean's husband, which was aggravated and magnified because the other person involved was her younger sister.

He ruled that stewards placed too much emphasis on McLean's previous misconduct conviction for assaulting another jockey and not enough on McLean's mental state at the time of the incident.

Judge Lewis also cited the unique circumstance at the time of the assault in which McLean, Beriman and her estranged husband were all present at Hamilton races.

McLean said she would now commit herself to repairing her relationship with her sister.

"I'm further committed to ensuring that the conduct of all riders in the female jockeys room is professional and in keeping with the work place standards."

She also called on her fellow riders to support she and her sister.