Instrument for girl (5)
I believe the answer is:
viola
I believe this clue is a double definition.
'instrument' is the first definition.
(I know that viola is a type of bowed stringed instrument)
'girl' is the second definition.
'for' acts as a link.
(Other definitions for viola that I've seen before include "Achievement" , "Shakespearean character" , "Bloomer" , "Flower -- stringed instrument" , "Page" .)