Girl not in love with an unknown author! (4)
I believe the answer is:
anon
'an unknown author' is the definition.
(short for an anonymous author)
'girl not in' is the wordplay.
'girl' becomes 'ann' (woman's name).
'not' becomes 'o' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'ann' going around 'o' is 'ANON'.
'love with' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for anon that I've seen before include "Mystery writer" , "At another time and with no identity, in short" , "Soon, shortly (archaic)" , "prolific author" , "Nameless - presently" .)