Declare her weight (8)
I believe the answer is:
announce
'declare her weight' is the definition.
(I've seen this before)
'her weight' is the wordplay.
'her' becomes 'ann' (I've seen this before).
'weight' becomes 'ounce' (ounce is a kind of weight**).
'ann'+'ounce'='ANNOUNCE'
(Other definitions for announce that I've seen before include "Report" , "Make public statement, proclaim" , "Disclose" , "Reveal" , "say" .)