Noblewoman's party venture (7)
I believe the answer is:
Here is my best explanation:
'noblewoman's' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'party venture' is the subsidiary indication.
'party' becomes 'do' (do is a kind of party).
'venture' becomes 'wager' (wager is a kind of venture).
(Other definitions for dowager that I've seen before include "Wordage (anag.)", "Titled widow", "woman of status", "Wordage for the widow of a peer", "Nobleman's widow", "Wealthy old woman", "elderly lady of means", "Widow with title or property from her husband", "Important widow" and "woman of property?".)