。
In the end, she went back to the UK.
Literal
She [topic-は] in-the-end UK [target-に] returned.
戻る ('to return, go back') always returns to a previous location, distinct from 帰る ('to go home, return to one's home base'). 戻る fits scenarios like reverting to a former residence, country, or job — anywhere one has been before that doesn't carry the 'home' framing of 帰る. イギリス is the standard Japanese name for the United Kingdom, originally borrowed from the Portuguese 'Inglez' (English) but now covering the whole UK in everyday usage. 結局 frames the move as the finale of an ongoing decision process.