The 53-year-old writer took Amanda Donaldson, 35, to court after sacking her for gross misconduct.
Rowling claimed Donaldson, of Coatbridge, Lanarkshire, wrongly benefited by spending on a company credit card and removing foreign cash from a safe.
A civil hearing at Airdrie Sheriff Court heard how Donaldson, who worked for Rowling between February 2014 and April 2017, treated the job as a “blank cheque” and bought a host of luxury items.
Sheriff Derek O’Carroll has now found in Rowling’s favour and ordered Donaldson to repay her £18,734.
A spokeswoman for the author said she was pleased with the outcome and intended to donate the money to her children’s charity Lumos.
Donaldson denied all wrongdoing insisting all the money had been used to buy items for the personal and business use of Rowling, who used her married name Joanne Murray in the action.
But the Harry Potter writer’s husband Dr Neil Murray described Donaldson as a “good liar” when he gave evidence in the case.
In a written ruling, the sheriff said Donaldson had obtained the money through “fraudulent misrepresentation” and had shown “persistent brazen dishonesty”.
He said: “I find the pursuer’s assessment of the pattern of fraudulent spending fits well with the rest of the evidence.
“I accept her evidence that it is inherently unlikely that the impugned expenditure was spent on her personally, her family or her business.
“I much preferred the evidence of the pursuer and that of her witnesses to that of the defender.
“I reject the oft-repeated evidence of the defender that the pursuer repeatedly and frequently asked her to buy things and that the pursuer repeatedly thanked the defender for items that she bought.
“The defender has shown herself capable of acting utterly dishonestly in relation to cash withdrawals using the credit card
and that finding significantly affects my conclusions on the reliability and credibility of her evidence.”
Sheriff O’Carroll said he had no doubts over the “credibility” and “reliability” of the evidence given by Rowling and her husband.
He said the Edinburgh-based writer gave her evidence “in a thoughtful, considered, measured, accurate, honest and reliable
The court heard Donaldson spent £823 at Bibi Bakery, £1482 with luxury candle company Jo Malone, £264 in Boots, £115 in Costa Coffee and £3629 in cosmetic firm Molton Brown.
She spent £117 in M&S Simply Food, £2139 in card shop Paper Tiger, £1636 in Starbucks and £235 in book store Waterstones.
She also bought two cats worth £1200 and also removed £7,742 of foreign money from a safe.
The sheriff described Donaldson’s explanations for the missing money as “incredible” and “highly implausible”.
He added: “Some of the defender’s evidence was inherently implausible or occasionally quite bizarre.
“For example, her claim that £3,600 on Molton Brown products was all spent on office supplies was quite unbelievable considering that it was the office manager’s job to supply such products and not hers, the annual cost of supplying the office with suitable products was only about £150 per year and she was specifically told by Dr Neil Murray that it was another’s job to buy such products.
“Her explanations as to the large and increasing amounts spent in coffee shops and bakeries was highly unlikely in my view, not least because she had her own well-equipped and stocked office to work in and no regular need to meet anyone in Edinburgh outside her office.
“There was no sound explanation as to why purchases from Boots were mostly unreceipted; that was not a coincidence in my view. She was seen loading large filled Paper Tiger bags into her car during working hours, which allegation though not denied, was never satisfactorily explained.”
Rowling had also claimed Donaldson stole Harry Potter merchandise worth more than £3200 but the sheriff ruled there was insufficient evidence to prove that.
In evidence, Donaldson insisted she had done nothing wrong and claimed Rowling was a ‘generous but not approachable’ employer.
She said: “I don’t lie, I’m not lying. It is not a very nice accusation to hear but I’m telling the truth.
“The job could be quite tense. There were frequent discrepancies which were really not needed but would happen.
“The job would be quite stressful as well.
“I was given the card through the post and Mrs Rowling ordered it for me and I was never told what to use it for.
“I would speak to the accountant and if he had any questions he would ask me but he was happy with what I was submitting.”
A spokeswoman for JK Rowling said: “JK Rowling is pleased that Sheriff O’Carroll has ruled that her former PA Amanda Donaldson must repay the money she fraudulently misappropriated from Ms Rowling.
“From the outset Ms Rowling made it clear that the decision to take this matter to court was a last resort and not for her personal benefit, but rather to protect the reputation of her existing staff, and to make sure Ms Donaldson is not in a position to breach the trust of another employer.
“Terms of the recovery will be decided in due course, and the money owed will be donated to JK Rowling’s charity Lumos.”
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