She claimed he pulled the towel down, partially exposing his penis and said, "are you looking for this?"
"I saw the top half of his penis, apologies, and I therefore shielded my view and left the change room," she told the court.
Ms Russell said afterwards she fled into the stands, "very upset."
"I was crying uncontrollably, I was crying like a child," she said.
"I was upset because of what Chris had done because we had known each other for 10 years and jokes of that nature meant nothing to him but upset me greatly."
Gayle gave evidence denying the allegations and said he was never in the change room wearing a towel.
His teammate, Dwayne Smith who was also in the change room at the time of the alleged incident, also denied Gayle exposed himself to Ms Russell.
Under cross-examination Smith admitted, however, that the previous day he had sent a text message to Ms Russell which said, "sexy," immediately before a massage session.
The trial heard Ms Russell went public with her allegations the following year after seeing Gayle's infamous sideline interview with sports journalist Mel McLaughlin when he told her, "don't blush baby".
"I was horrified because I saw how uncomfortable Mel McLaughlin was," she said.
She said she as furious that, "women who work hard in this industry are made to feel that way both on camera and in the change room and that people like Chris get to decide whether we are successful or not".
Gayle said the articles were, "the most hurtful thing I have actually come across in my entire life".
His close friend and professional cricket coach Donovan Miller gave evidence that Gayle was now scared to be around women.
Mr Miller said Gayle had become very reserved "and scared, especially (around) females and he always feels someone is out to get him".
Gayle's barrister Bruce McClintock accused Ms Russell of making the story up.
He suggested to Ms Russell that she and West Indies physiotherapist, CJ Clarke, who had an ongoing feud with Gayle, colluded to make up the story so the cricketer would be kicked out of the team.
"Absolutely untrue," Ms Russell said.
The court heard allegations Clarke had challenged Gayle to a fight during the West Indies tour of South Africa in 2015.
Clarke also sent Ms Russell a text message the day after the Mel McLaughlin interview suggesting that she should put in her "two cents."
The following day when the allegations were published Clarke texted Ms Russell, "you little beauty, well done".