Mia Davies says she is "disappointed" it took so long for the investigation into Catherine Marriott's complaint - made in February - to be finalised.

"The fact there had been no real finding after all this time will no doubt act as a deterrent for anyone else with genuine complaints to come forward in future," she said in a statement Friday evening.

Ms Marriott's complaint led Mr Joyce to resign as deputy prime minister and leader of the Nationals.

The West Australian farmer was told on Thursday that after an eight-month investigation, the NSW branch of the Nationals had been unable to make a determination about the case because of "insufficient evidence".

Ms Davies said the WA branch of the The Nationals takes "such matters extremely seriously" and that since receiving Ms Marriott's initial complaint and referring it to the federal secretariat, the WA state executive had examined its own processes for dealing with future complaints.

From now on the WA branch would use an independent third party to manage the complaints in a confidential manner, Ms Davies said.

"At a time where the culture and behaviour of those involved in politics is under justifiable scrutiny it is incumbent on all of us to work harder to ensure our organisations are respectful and safe places to work, and that we set the best example possible at all times," she said.

An "extremely disappointed" Ms Marriott said in a statement Friday she was not surprised at the result because the party had no plans for how to handle a sexual harassment complaint against an MP.

"This is despite the investigation finding I was "forthright, believable, open and genuinely upset" by the incident," Ms Marriott said.

She made three trips to the east coast at her own expense to meet with the party and her name and confidential complaint were leaked to the media.

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

"I am pleased I stood up for what I believed was right."

Mr Joyce stood down in February after Ms Marriott's allegations were raised, describing them as the last straw.

He was already under pressure to resign following his affair with ex-staffer Vikki Campion, with whom he now has a child.

Mr Joyce later said he knew he would have to resign once Ms Campion got pregnant but he hung on out of spite as the government bled support.

Ms Marriott said the only positive to come from "this harrowing experience" has been the Nationals' development of a much-improved policy for dealing with complaints.

The Nationals released a statement on Friday revealing the investigation was complete but the result would stay confidential.

Australian Associated Press