
I also speak two languages. People usually slip into another language when they’re more comfortable or get very passionate or angry. My gf has her grandma over rn and she’s saying shit because they slip into Spanish and she’s paranoid they gossip about her. It’s impossible to know without hearing it.
If she grew up speaking her secondary language at a young age, she may slip into it if she’s talking about a boy or family business. Not always exactly trying to avoid you. If she began taking her second language recently, she may be showing her family or maybe a new family member takes the phone and she jumps into the other language.