Preferably, the woman’s pursuing betrayer (6)
I believe the answer is:
rather
'preferably' is the definition.
(I know that preferably can be written as rather)
'woman's pursuing betrayer' is the wordplay.
'woman' becomes 'her' (her refers to a woman).
'pursuing' is a charade indicator (letters next to each other).
'betrayer' becomes 'rat' (synonyms).
'her' after 'rat' is 'RATHER'.
'the' acts as a link.
(Other definitions for rather that I've seen before include "Slightly, more so than not (6" , "Pretty" , "Yes, please!" , "Most certainly" , "somewhat > sooner? > Quite" .)