Her music so confused a section of the choir (10)
I believe the answer is:
semichorus
'a section of the choir' is the definition.
'her music so confused' is the wordplay.
'confused' is an anagram indicator.
'her'+'music'+'so'='hermusicso'
'hermusicso' anagrammed gives 'SEMICHORUS'.
(Other definitions for semichorus that I've seen before include "singing group" , "Part of a choir" , "Singers" .)