She contributes to one's irritation (4)
I believe the answer is:
rita
'she' is the definition.
'contributes to one's irritation' is the wordplay.
'contributes to' indicates a hidden word (I've seen 'contributing to' mean this (the answer contributes to part of the clue )).
'RITA' can be found hidden inside 'ones irritation'.
(Other definitions for rita that I've seen before include "Educating - - , film" , "Lovely -- , meter maid (Beatles)" , "The Beatles' lovely girl" , "-- Hayworth, US film actress" , "...Hayworth, ...Coolidge, ... ''Educating ...''" .)