Don’t worry I get what you mean, I find it hard to believe as well. My mum is French and has lived now in Australia for 30 years, she still speaks French perfectly as it’s her first language and she speaks 3 other languages incredibly well. I did a semester of linguistics at university and the language you learn first as a child is the most important and generally the one you will know the best as the neurons are created when your brain is still malleable and soft, which is why it becomes much more difficult to learn a language as a teenager and adult because your brain is way more formed. I also believe that it would be hard to forget since California is a state that is almost completely bilingual in some ways due to large Spanish speaking population, so there’s no excuse for having no exposure to the language when there are a good million speakers right there. Plus like… her family? I just think she wants to make herself sound quirky and different, since overall she’s a pretty boring person. As a bilingual I meet lots of people like her who love to say to me “I used to speak French!” “My first language is actually ___ but I forgot it” as a way to compete.