Cr John Burns instigated the investigation just days after he was elected in the Division 4 by-election, alleging Cr Bowler had slandered council officials when she described their report into her application as "questionable" to the Courier Mail.

A second complaint was made by an unnamed person, alleging Cr Bowler had tried to influence other councillors to vote in her favour.

Both the claims have been dismissed by the CMC, with a CMC spokesperson saying "unless new evidence is provided, we will not be pursuing this case".

"The case was investigated and assessed and it was decided it did not warrant any further investigation," the spokesperson said.

"There was no evidence of official misconduct that we could move forward with, and the matter has been handed back to the council's CEO to act as he sees fit."

Councillors voted for the extension despite council officers recommending it not be granted, because a number of zoning requirements had changed in the area since the DA was first lodged nearly nine years ago.

Cr Bowler said she was extremely happy with the outcome, but concerned it may not be the end of a "mischievous campaign".

"I've owned that property for 31 years and I know the councillors just made a commonsense decision," Cr Bowler said.

"This was a smear campaign initiated by a candidate who failed to get re-elected (in 2008), trying to discredit good, community-minded councillors who were successful as they had the support of the community who wanted change.

"It's just vindictive payback and I give the community credit for seeing through it all.

"We have so many important and good things to do for this community, and so much time was wasted on this."

Cr Bowler said her motion at this week's general meeting to commission an audit of development application decisions over the past 12 months was not related to this decision, but a response to community concern about non-compliant developments that may have been approved.