About to lose strength, daughter went to bed (7)
I believe the answer is:
retired
'went to bed' is the definition.
('retire' can be a synonym of 'go to bed')
'about to lose strength daughter' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to lose strength' becomes 'tire' (tire can mean to run out of strength).
'daughter' becomes 'd' (genealogical abbreviation).
're'+'tire'+'d'='RETIRED'
(Other definitions for retired that I've seen before include "out of office?" , "Went to bed or gave up work" , "claiming a pension?" , "Ceased working" , "In bed, withdrew" .)