You mean, like wholly unaccented and perfectly colloquial Mila Kunis, who emigrated from the Ukraine at age 7 (BBM)?
https://www.biography.com/actor/mila-kunis
If Natalia had had Russian speakers to practice with in the U.S. also, she might not have forgotten her Russian. Nothing that I've read so far indicated that she did get that chance.
BBM, what's convincing about this alleged detective's invoking the government? That all sounds rather silly to me. Homeland Security is allegedly worried about a girl who's been in the United States for a dozen years, has no money to go anywhere or do anything - are we supposed to believe "Homeland Security" is on her trail because it thinks Natalia is, what, a spy?
Willing to admit I'm no student of government, thus happy to be corrected on the purpose of DHS in this country; but still, I don't find any of that rings true. It rather more sounds to me like Kristine should switch to writing novels; and in the interest of practicality, we know she wouldn't be the first "nonfiction" writer to get called out for embroidery, embellishing, or just plain making things up (James Frey, Augusten Burroughs, Rigoberta Menchu, others linked below)?
Five Big Fat Literary Fakes
IMO, MOO, but I find the inclusion of the DHS in KB's story to be laughable. Aim lower than a shadowy conspiracy topped off with invocation of the federal government, lady! SMH...