She'd already dropped 36kg, but Heather Albert was left in tears after her first trip to Lululemon.
The American mum, who had weight loss surgery last year, said she was "pretty proud of myself" after getting into shape and wanted to treat herself a pair of the brand's fancy, expensive yoga pants.
"When my amazing fiancee heard I was going to Park City, Utah for a work trip this past week, she insisted I go to the retail store in PC and buy myself something," Ms Albert wrote on Facebook.
"I dropped my co-workers off at our hotel and ran over to the store to see what they had."
While perusing the sales rack, she said, a staff member could be heard whispering loudly to her colleague: "Do we even have anything in her size?" before bursting into laughter.
"I was the only customer in the store," Albert wrote. "I knew it was directed at me.
I was mortified. I quickly bought the two things I had in my hand that I had found and left the store. I was so embarrassed! I had a work function to go to that night, when I got back to my hotel I cried in the shower."
he said that while "not everyone fits into Lulu", at a US size 10/12 (Australian size 14 to 16) I'm not even close to maxing out on size there!"
In a testament to the brand's allure, rather than threatening to boycott Lululemon, Albert said she would "stick to the outlets and online shopping from now on".
A Lululemon representative apologised to Albert for her experience and promised to "dig into this further and help to make things right".
The incident comes as the global activewear company, which has 25 stores in Australia, ploughs millions of dollars into its local operation in a bid to steal market share from competitors like Lorna Jane, which has 200 stores - and is also known for its controversial stance on body size.
The company's latest financial accounts show that it invested $19.73 million into its Australian business in the 2016 financial year, Fairfax Media reports.
The strategy, which includes a national marketing blitz, appears to have worked. Lululemon Australia transformed its financial performance in 2016, turning a $6.8 million profit - in contrast to the previous year's $7.2 million loss.
Annual sales grew by 16 per cent to $98 million in what is the company's third biggest market outside of the United States and its native Canada.