Widow has bet after party (7)
I believe the answer is:
dowager
'widow' is the definition.
(term for an aristocratic widow)
'bet after party' is the wordplay.
'bet' becomes 'wager' (synonyms).
'after' says to put letters next to each other.
'party' becomes 'do' (do can informally mean a party).
'wager' put after 'do' is 'DOWAGER'.
'has' acts as a link.
(Other definitions for dowager that I've seen before include "Rich old girl" , "woman of status" , "woman of property?" , "Widow, imposing elderly woman" , "Titled widow" .)