。
She has been abroad ever since.
Literal
She [topic-は] that-after continuously foreign-country [in-に] is.
その後 ('after that, since then') sets the reference point. ずっと ('continuously, all this time, the whole time') is a vivid intensifier of duration — emphasizing unbroken continuity. The plain present いる describes ongoing existence/presence; combined with ずっと, it captures 'has been [there] all this time.' に marks the location. The whole sentence is the kind of biographical line that follows a notable departure: 'and after that, she's been overseas all along.'