A one-way girl (4)
I believe the answer is:
anne
'girl' is the definition.
(girl's name)
'a one-way' is the wordplay.
'one way' becomes 'nne' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'nne'='ANNE'
Can you help me to learn more?
(Other definitions for anne that I've seen before include "First queen of Great Britain and Ireland" , "Female name" , "Boleyn or Hathaway, say" , "Second or fourth wife of Henry VIII" , "One of the Bronte' tens" .)