Indeed, Susan's about right! (4)
I believe the answer is:
sure
'indeed' is the definition.
(thesaurus)
'susan's about right' is the wordplay.
'susan' becomes 'sue' (short for Susan).
'about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'sue' enclosing 'r' is 'SURE'.
(Other definitions for sure that I've seen before include "Positive" , "Feeling no doubt" , "stable" , "certainly in the USA" , "See 12" .)