The old lady, you bet, will be going to the party (7)
I believe the answer is:
dowager
'the old lady' is the definition.
(I've seen this before)
'you bet will be going to the party' is the wordplay.
I cannot quite understand how this works, but
'bet' could be 'wager' (synonyms) and 'wager' is located in the answer.
'party' could be 'do' (do is a kind of party) and 'do' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dowager that I've seen before include "Rich old woman" , "Wordage (anag.)" , "elderly lady of means" , "Wealthy old woman" , "Wordage for the widow of a peer" .)