Pardon the awkward phrasing in the title, but I am essentially wondering about the following scenario.
A person, Alice, grows up bilingual, speaking languages A and B. She lives in a country C in which the national language is A, but her social circle is primarily people who grew up in country D whose native language is B. She has no B-accent when speaking language A. Alice then moves to D, and now speaks B almost 100% of the time with other native speakers. A few years later, she appears to have adopted not only a B-accent when speaking A (subtle, but heard by native speakers of A), but also certain broken-A phrases common for people whose first language is B and second language is A. That is, she now speaks A as if it is her second language, albeit still fluently.
My question is then: is such a phenomenon well-known? Where can I read more about it, if so?
More generally, to what extent does one's environment affect fluency of one's native language?