That woman’s lad turned out to be a courier (6)
I believe the answer is:
herald
'a courier' is the definition.
(herald is a kind of courier)
'that woman's lad turned out' is the wordplay.
'that woman' becomes 'her' (I've seen this before**).
'turned out' is an anagram indicator.
'lad' is an anagram of 'ald'.
'her'+'ald'='HERALD'
'to be' acts as a link.
(Other definitions for herald that I've seen before include "Proclaim the approach of, like old messenger" , "Announcer - forerunner" , "College of Arms official" , "Scottish newspaper" , "Proclaim the approach of, like archaic messenger" .)