Special bath for a girl with sex appeal (5)
I believe the answer is:
sauna
'special bath' is the definition.
'a girl with sex appeal' is the wordplay.
'a girl' becomes 'una' (**).
'with' is a charade indicator (letters next to each other).
'sex appeal' becomes 'sa'.
'una' after 'sa' is 'SAUNA'.
'for' is the link.
(Other definitions for sauna that I've seen before include "Room for steam bath" , "Form of steam bath" , "Type of bath" , "Steam-heated room" , "Very hot cleansing room from Finland" .)