She turned me against the master (4)
I believe the answer is:
emma
'she' is the definition.
(I've seen this before)
'turned me against the master' is the wordplay.
'turned' says the letters should be written backwards.
'against' means one lot of letters go next to another.
'the master' becomes 'ma'.
'me' back-to-front is 'em'.
'em'+'ma'='EMMA'
(Other definitions for emma that I've seen before include "Novel by June Austen" , "Girl's name - Jane Austen novel" , "Mrs Bovary" , "young woman in novel" , "Titled heroine" .)