Female fool in AA (5)
I believe the answer is:
anita
'female' is the definition.
(I've seen this before)
'fool in aa' is the wordplay.
'fool' becomes 'nit' (both can mean a stupid person).
'in' indicates putting letters inside.
'nit' inserted into 'aa' is 'ANITA'.
(Other definitions for anita that I've seen before include "Female" , "eg Dobson or Roddick" , "lady" , "girl produced" , "Woman" .)