Mockery McDonald’s

My mom ordered a chicken burger and complained that the patty was dry from her first bite. She was famished and far from the store she bought it from and finished it. The same day and onto the next day she had an upset tummy. She returned to the store (Welkom) and a lady, with short hair mocked her and said she probably shouldn’t have eaten the burger and was allergic to lettuce - my mom has no such allergies and made no mention of that, she just said patty was dry and she fell ill. Cashier or manager, same lady with short hair mocked my mother further by telling her she should have came back with a Drs note stating the burger caused her illness. It was so unprofessional and insulting to my mom who still gave the shop business that same day by buying drinks and sweet corn for my son. I am very upset.