Relative in Riviera resort, reportedly (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'in riviera resort reportedly' is the wordplay.
'in' indicates putting letters inside.
'riviera resort' becomes 'nice' (I've seen this in another clue).
'reportedly' becomes 'e' (I've seen this in other clues).
'nice' going around 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Brother or sister's daughter" , "Female family member" , "Brother's girl" , "girl further down the line" , "A sibling's daughter" .)