Satnam Kaur, 30, took the money from Robert Brown, who worked in the oil and gas industry, while an adviser at the bank's branch in Albyn Place, Aberdeen, over one month in 2011.
Kaur had claimed during her trial at Aberdeen Sheriff Court that Mr Brown had gifted her the money because she had threatened to report him to the police for allegedly touching her inappropriately.
However, this was described as a "pack of lies" by the prosecution and Sheriff Christopher Shead described her account as incredible, finding her guilty of theft.
Using her unique identification number, Kaur transferred several large sums from Mr Brown's bank accounts to another man, named as Robert Mann, totalling £120,000, the court heard. A cheque was then written out for the same amount in the name of Mr Mann to Kaur's Lloyds TSB account.
Both men said they had not given Kaur permission to access their accounts.
Some of the cash was sent to her home country of India and she gave £1,000 to a friend.
None of the cash can be recovered but Mr Brown has since been reimbursed by the bank.
Kaur was also found guilty of removing £88,000 of the cash out of Scotland and is to be deported.
Sentence was deferred until later this month for background reports.