An eight-month investigation into a complaint of sexual harassment against the former deputy prime minister Barnaby Joyce has been unable to reach a determination, according to the woman who lodged it, Catherine Marriott.

Marriott issued a statement on Friday saying the New South Wales Nationals had emailed her on Thursday to advise they had “been unable to make a determination about my complaint of sexual harassment against the former leader of that party … due to insufficient evidence”.

The NSW Nationals issued a brief statement confirming the sexual harassment investigation had been finalised, and saying the report would be kept confidential.

Marriott expressed fury with the result of the inquiry. “This outcome simply isn’t good enough,” she said. “I’m extremely disappointed that after eight months of waiting, three trips to the east coast at my own expense to meet with the party, my name and confidential complaint being leaked to the national media, and my personal and professional life being upended, the National party have reached a no-conclusion verdict.”

She said while furious with the outcome, she was not surprised, because she did not consider the Nationals to have “the external processes in place to deal with a complaint of sexual harassment by a member of parliament”.

Marriott said she believed the complaint – which Joyce has consistently denied – had been handled internally by the state executive “with no professional external expert brought in at any stage to handle the matter”.

She said the only positive to emerge from the experience was the National party now had a framework to manage complaints.

“While it has come at enormous personal expense, I was not prepared to walk past this kind of behaviour any longer,” Marriott said.

“I am pleased I stood up for what I believed was right and I’m proud I found the courage to make a difference for other people who want to create influence through political circles in future”.

Marriott made the complaint against Joyce in February, and it proved the trigger for his resignation from cabinet. Joyce, then in the middle of a furore about the end of his marriage and a new relationship with a former staffer, told reporters the harassment complaint had contributed to his decision to step down. “It’s quite evident that you can’t go to the dispatch box with issues like that surrounding you,” he said.

After Marriott lodged her complaint on 20 February, initially with the National party’s federal executive, it was leaked to the media a few days later.

At the time Joyce said the claim was “spurious and defamatory” and said he had asked for it to be referred to the police.

After her name was leaked to the media, friends and colleagues rallied to Marriott’s defence. Marriott is a former West Australian Rural Woman of the Year.

The president of Australia’s most powerful rural body, the National Farmers Federation, backed Marriott and suggested the Nationals had leaked against her. Fiona Simson described Marriott as “undeniably one of the most fair dinkum people I know”.

“She is generous, passionate and honest. Whatever she says goes. Hugely courageous. She wanted to give the Nats a chance to sort it out and they leaked instead,” Simson said.