Excellent, so knight saves student girl (6)
I believe the answer is:
alison
'girl' is the definition.
(girl's name)
'excellent so knight saves student' is the wordplay.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'knight' becomes 'n' (chess abbreviation).
'saves' is an insertion indicator.
'student' becomes 'l' (as in L-plates for learner drivers).
'ai'+'so'+'n'='aison'
'aison' going around 'l' is 'ALISON'.
(Other definitions for alison that I've seen before include "Girl's name" , "female" , "woman" , "lady" , "Girl" .)