Actress being with it and set on fire (7)
I believe the answer is:
hepburn
'actress' is the definition.
(I've seen this before)
'with it and set on fire' is the wordplay.
'with it' becomes 'hep' (old-fashioned spelling of 'hip', meaning trendy).
'and' is a charade indicator (letters next to each other).
'set on fire' becomes 'burn' (I've seen this before).
'hep'+'burn'='HEPBURN'
'being' acts as a link.
(Other definitions for hepburn that I've seen before include "Audrey --, film actress" , "Audrey and Katherine, film stars" , "See 9" , "Audrey -; Katharine -, film actresses" , "Audrey and Katharine, film stars" .)