Principal admits she's wrong about religious education (12)
I believe the answer is:
headmistress
'principal' is the definition.
(headmistress is a kind of principal)
'admits she's wrong about religious education' is the wordplay.
'wrong' indicates an anagram.
'about' means one lot of letters goes inside another.
'religious education' becomes 're'.
'admits'+'shes'='admitsshes'
'admitsshes' anagrammed gives 'headmistss'.
'headmistss' placed around 're' is 'HEADMISTRESS'.
(Other definitions for headmistress that I've seen before include "Female school leader" , "Teacher" , "Person in charge of a school" , "School principal" .)