She's in Britain (4)
I believe the answer is:
rita
'she's' is the definition.
'in britain' is the wordplay.
'in' indicates the answer is hidden within the clue.
'RITA' is hidden in the letters of 'britain'.
(Other definitions for rita that I've seen before include "-- Hayworth, US film actress" , "Lovely -- , meter maid (Beatles)" , "subject of education" , "The Beatles' lovely girl" , "Educating - - , film" .)