Garland has new role in Siren? (7)
I believe the answer is:
lorelei
'siren?' is the definition.
(I know that Lorelei is a Siren)
'garland has new role' is the wordplay.
'garland' becomes 'lei' (synonyms).
'has' is an insertion indicator.
'new' is an anagram indicator.
'role' is an anagram of 'orel'.
'lei' placed around 'orel' is 'LORELEI'.
'in' acts as a link.
(Other definitions for lorelei that I've seen before include "voice to die for" , "Rhine rock famed for siren" , "Bloody singer" , "Fatal attraction" , "High rock in the Rhine gorge" .)