A pop group -- one daughter's rejected (9)
I believe the answer is:
abandoned
'rejected' is the definition.
(I've seen this before)
'a pop group one daughter's' is the wordplay.
'pop group' becomes 'band' (I've seen this before).
'daughter' becomes 'd'.
'a'+'band'+'one'+'d'='ABANDONED'
(Other definitions for abandoned that I've seen before include "Deserted - shameless" , "Rejected" , "Obsolete" , "Deserted; uninhibited" , "lacking in self-control" .)