Girl from Pinner is sacked (7)
I believe the answer is:
nerissa
'girl' is the definition.
'from pinner is sacked' is the wordplay.
'from' says the answer is hidden in the clue.
'NERISSA' is hidden in the letters of 'pinner is sacked'.
(Other definitions for nerissa that I've seen before include "Girl from Belmont" , "Portia's attendant" , "One working for Portia" , "Serving maid" , "Lawyer's clerk apparently" .)