Daughter should, before end of day, be resolute (7)
I believe the answer is:
doughty
'resolute' is the definition.
(I've seen this before)
'daughter should before end of day' is the wordplay.
'daughter' becomes 'd'.
'should' becomes 'ought' ('ought' can be a synonym of 'should').
'before' says to put letters next to each other.
'end of' suggests the final letters.
The last letter of 'day' is 'y'.
'd'+'ought'+'y'='DOUGHTY'
'be' is the link.
(Other definitions for doughty that I've seen before include "Stout-hearted, valiant" , "Brave, resolute (arch.)" , "Fearless" .)