A magistrate has scolded a 45-year-old Boulder woman for wasting police resources after she made up a sexual abuse allegation against an innocent Perth taxi driver.

Allison Louise Reardon told police she had been sexually assaulted in June, sparking an investigation by detectives from the Sexual Assault Squad.

But Reardon, who was attending a work conference in Perth at the time, has now been fined $4,000 in the Kalgoorlie Magistrates Court after pleading guilty to creating a false belief.

The court heard Reardon became upset after she claimed the driver took the long way to her destination during her 12-minute taxi ride.

She allegedly tried to break the driver's identification card before she eventually called triple-0, with the recording tabled as evidence.

In the call, Reardon was telling the operator about the dispute and was asked if there was anything life-threatening occurring.

"Well, he sexually assaulted me," she replied.

Reardon claimed the driver had placed his hands down her pants, on top of her underwear.

But detectives reviewed closed-circuit television footage and found the assault never took place.

"The CCTV footage shows the driver did not assault the woman as she described," police prosecutor Senior Constable Thomas Banyard told the court.

Reardon's lawyer Carmel McKenzie told the court her client suffered from "a number of mental health issues" and had been taking anti-depressant medication for the past 10 years.

Ms McKenzie said her client's medication had been changed and she had also been placed on blood pressure medication for other health issues.

"She had been struggling at that time and in fact her husband did not feel she was well enough to attend the conference, but she didn't want to let her employer down," Ms McKenzie said.

Taxi driver 'just doing his job': magistrate

Ms McKenzie said Reardon had consumed some alcohol at a work function over a period of about 90 minutes before getting into the taxi.

Reardon became upset after the taxi driver allegedly took a long route, the court heard. ( ABC News: Gary Rivett )

She said Reardon was "disorientated", "confused" and "not cognisant".

But during sentencing, Magistrate Adam Hills-Wright told Reardon there was no evidence to suggest there was a connection between her alcohol consumption and medication that reduced her "moral culpability".

He said it was a "serious example" of the offence, which can carry a maximum sentence of up to 12 months' jail and a $12,000 fine.

Mr Hills-Wright said the taxi driver was just "doing his job".

"You've placed this driver in anybody's worst nightmare … it is anybody's worst nightmare where they are falsely accused of a sexual crime," he said.

"You maintained this lie over several hours while speaking to the triple-0 operator, police and even the Sexual Assault Squad.

"They are a specialist squad for bona fide abuse cases, and you wasted their resources."

Reardon will also be required to pay $480.34 in reparations for police overtime and $198 in court costs.