Helen McMahon often worked 12-hour days without a lunch break, an employment tribunal said.
In a meeting with Heron’s CFO Robin Thomas in May 2019 Ms McMahon, who was earning £ 27,000 a year, complained about her hours, commission and sick pay.
She told the court: “I said I was working more than 48 hours a week, it was stressing me out, and I kind of wanted to cut back on my hours.
Two days later Ms McMahon was fired by founder Warren Harrocks, without explanation.
The company, of Rickmansworth, Herts, told the court she had been fired due to performance issues – although they offered her a bottle of champagne as a reward for her work that year.
Mr Harrocks also said he was not aware of any grievances expressed at his previous meeting.
But a text from Mr Thomas to one of his colleagues said Ms McMahon was “still moaning.”
Cambridge judge Sarah King ruled that she had been unfairly dismissed and awarded her a total of £ 23,000.
She said: “It is clear that (Heron Financial) considered (Ms McMahon) to be a ‘moaner’ – someone who complained.
“Her dismissal was because she was ‘moaning’. This was unfair because no procedure was followed and there was no valid reason to terminate. “