Girl has weight to declare (8)
I believe the answer is:
announce
'declare' is the definition.
(I know that declare can be written as announce)
'girl has weight' is the wordplay.
'girl' becomes 'ann' (woman's name).
'has' is a charade indicator (letters next to each other).
'weight' becomes 'ounce' (ounce is a kind of weight).
'ann'+'ounce'='ANNOUNCE'
'to' acts as a link.
(Other definitions for announce that I've seen before include "say" , "Reveal" , "Formally declare" , "Give public notice to" , "Make known officially" .)