...(a less messy-sounding girl) (5)
I believe the answer is:
anita
'sounding girl' is the definition.
'Anita' can be an answer for 'girl'. I'm not sure about the 'sounding' bit.
'a less messy' is the wordplay.
'less messy' becomes 'nita' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'nita'='ANITA'
Can you help me to learn more?
(Other definitions for anita that I've seen before include "lady" , "girl produced" , "-- Loos, US writer" , "eg Dobson or Roddick" , "Woman" .)