Elisabetta Grillo, 41, took ill and had to be led from the dock at Isleworth Crown Court, London, as evidence about her was given by her former colleague Alice Binks.
The defendant and her sister, Francesca Grillo, 35, are accused of abusing their positions by spending £685,000 on credit cards belonging to the celebrity couple to buy designer goods and luxury holidays for themselves. They each deny a single count of fraud.
Elisabetta returned to the courtroom after a brief break, wiping her face with a tissue.
Ms Binks, who also worked as a personal assistant to Ms Lawson during her marriage to Mr Saatchi, said she often noticed the sisters wearing expensive-looking clothes and with designer handbags.
"Francesca would say she got them from, like, a thrift shop or from eBay at a heavy discount," said Ms Binks, who now works for ITV.
"Elisabetta always had nice handbags. She would always say they were from discount stores.
"They were always quite cagey and would sometimes get angry if you asked what they had done at the weekend and were always quite secretive about their personal lives."
Ms Binks said Elisabetta - also known as Lisa - "could be quite difficult to work with". She added: "She was quite bitter and quite angry.
"Most of the time Lisa would be on Facebook."
The trial continues.