My girlfriend said that eating onions will protect you

The other day, I brought up the topic with my girlfriend, and while discussing “what would happen if we didn’t use protection,” she suddenly said, “onions strengthen the immune system, kill germs, nothing will happen.” Was she joking? I couldn’t tell if she was serious. I felt a bit embarrassed and couldn’t continue talking openly. Is this level of ignorance normal? Who spreads such urban legends?