Relative's sweet embracing sweetheart (5)
I believe the answer is:
niece
'relative's' is the definition.
(niece is a kind of relative)
'sweet embracing sweetheart' is the wordplay.
'sweet' becomes 'nice' (I've seen this in other clues).
'embracing' is an insertion indicator.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'nice' going around 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Preparation for curdling milk" , "Son's cousin" , "Brother or sister's daughter" , "Kinswoman" , "One of the family" .)