Very sweet woman’s engaged in applying the third degree? (8)
I believe the answer is:
cherubic
'very sweet' is the definition.
'woman's engaged in applying the third degree?' is the wordplay.
'woman' becomes 'her' (pronoun for a woman).
'engaged in' is an insertion indicator.
'applying the third degree?' becomes 'cubic' (cubing is multiplying a number to the power of 3).
'her' placed into 'cubic' is 'CHERUBIC'.
(Other definitions for cherubic that I've seen before include "heavenly" , "Angelic, seraphic" , "Angelically innocent" , "Having a plump innocent face" , "Sweet" .)