She casts a spell in French song about ship (11)
I believe the answer is:
enchantress
'she casts a spell' is the definition.
I can't judge whether this definition defines the answer.
'in french song about ship' is the wordplay.
I cannot quite understand how this works, but
'song' could be 'chant' (song sung by a crowd) and 'chant' is present in the answer.
'about' could be 're' ('re' means regarding or about) and 're' is found in the answer.
'ship' could be 'ss' (prefix in ship names eg SS Great Britain) and 'ss' is located in the answer.
'in french' could be 'en' ('in' in French) and 'en' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for enchantress that I've seen before include "Siren" , "Female magician" , "Witch" , "One casting spells" , "Bewitching female" .)