A girl who takes the right part (6)
I believe the answer is:
esther
'a girl' is the definition.
'takes the right part' is the wordplay.
'part' indicates the answer is hidden within the clue.
'ESTHER' can be found hidden inside 'takes the right'.
'who' acts as a link.
(Other definitions for esther that I've seen before include "OT heroine" , "10 Heroine" , "Oratorio by Handel; girl's name" , "Beautiful lady" , "Old Testament book that tells of a beautiful Jewess" .)