A girl is after one, right? (4)
I believe the answer is:
iris
'a girl' is the definition.
'is after one right?' is the wordplay.
'after' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral**).
'right?' becomes 'r' (common abbreviation).
'i'+'r'='ir'
'is' after 'ir' is 'IRIS'.
(Other definitions for iris that I've seen before include "Flag,flower and part of the eye" , "A flower; spirit conjured in Tempest" , "Flag - flower - girl" , "Eye part or attractive flower" , "Film about writer _______ Murdoch" .)