Sacking for girl’s prayer book (9)
I believe the answer is:
dismissal
'sacking' is the definition.
(synonyms)
'girl's prayer book' is the wordplay.
'girl's' becomes 'dis'.
'prayer book' becomes 'missal' (missal is a kind of prayer book).
'dis'+'missal'='DISMISSAL'
'for' acts as a link.
(Other definitions for dismissal that I've seen before include "Release - marching orders!" , "Notice" , "removal from office" , "job loss?" , "Process of being sent away" .)