The support of a very good daughter (3)
I believe the answer is:
aid
'the support' is the definition.
('aid' can be a synonym of 'support')
'a very good daughter' is the wordplay.
'a very good' becomes 'ai' (**).
'daughter' becomes 'd'.
'ai'+'d'='AID'
'of' acts as a link.
(Other definitions for aid that I've seen before include "Help or support" , "welfare" , "Care, assistance" , "assistant" , "charity" .)