Lol dude, come on... I'm bilingual, and know a lot of bilingual people. I've seen people have mental blanks in their original language if they've been speaking English for a long time, for example. Stuff like that is normal if they move back. Developing an accent in your original language if you're speaking something else 24/7 is not out of the realm of possibility. It's common with regional accents. People come back with a different accent after living in a different state for a while, then it goes back to normal. Why would it be so impossible for the same thing to happen with a different country instead of a different state?
Do you or those people have any evidence to say this is intentional? It doesn't make sense, and you're acting like it's 100% certain. Your theory about her trying to ingratiate herself with Brazilians is silly, most of them can't even understand English, so they can't tell if she has an accent or not in English. I'm bilingual and I'm around people who share 2 cultures pretty frequently. I don't know a single person who would look at you differently if you speak English without an accent (especially if they know you're American, lol), as long as you can communicate with them in their own native language. Even guys who don't speak the second language at all (Cain Velazquez) are celebrated. No clue of where you're getting that idea from.