I grumble over girl (5)
I believe the answer is:
naomi
'girl' is the definition.
'i grumble over' is the wordplay.
'grumble' becomes 'moan' (I've seen this before).
'over' says the letters should be written backwards.
'i'+'moan'='imoan'
'imoan' in reverse letter order is 'NAOMI'.
(Other definitions for naomi that I've seen before include "Ruth's mother-in-law (OT)" , "- - Campbell, supermodel" , "OT female" , "Biblical mother-in-law of Ruth" , "-- Campbell, British model" .)