The writer grumbles about girl (5)
I believe the answer is:
naomi
'girl' is the definition.
(girl's name)
'the writer grumbles about' is the wordplay.
'the writer' becomes 'I' (the person who is writing these clues).
'grumbles' becomes 'moan' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' says the letters should be written backwards.
'i'+'moan'='imoan'
'imoan' written backwards gives 'NAOMI'.
Can you help me to learn more?
(Other definitions for naomi that I've seen before include "Relative of Ruth" , "Biblical woman" , "OT female" , "Ruth's mother-in-law (Bible)" , "Do I moan about Biblical Ruth's mother-in-law?" .)