Narendra Gill, aged 52, of York, was jailed for 28 months after she tried to swindle £130,000 from a pensioner after claiming he had a losing lottery ticket.
Leeds Crown Court heard that Gill swiped the EuroMillions lucky dip ticket from retired deliveryman Frank Gowland after checking it at her shop in Leeds.
The 81-year-old did not realise he had a winning ticket – which had five winning numbers and a Lucky Star – until police told him it was stolen a few weeks later.
Staff at Camelot, which runs the lottery, became suspicious when Gill called them to check the ticket and they heard her serving customers at her GT News shop.
She admitted to working in the now-closed GT News shop at the White Rose Shopping Centre.
But she claimed she was gifted the lottery ticket and did not know where it was bought.
Camelot called the police. Officers identified Mr Gowland via CCTV footage, spotting him and his wife Sue getting into a car at the shopping centre.
Gill admitted theft and fraud.
Recorder Dafydd Enoch QC told her she had been “unbelievably cruel”.
He added: “People who work in these places need to hear the message that you cannot abuse your position when it comes to dealing with millions of pounds. Trust is so important.”