A bookish girl (4)
I believe the answer is:
nana
'girl' is the definition.
'a bookish' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
The remaining letters 'na' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for nana that I've seen before include "Grandmother - dog in Peter Pan" , "Old woman" , "Grandma" , "Informal grandmother" , "Idiot" .)