Yes, her strange, unorthodox belief (6)
I believe the answer is:
heresy
'unorthodox belief' is the definition.
(I've seen this before)
'yes her strange' is the wordplay.
'strange' indicates anagramming the letters.
'yes'+'her'='yesher'
'yesher' anagrammed gives 'HERESY'.
(Other definitions for heresy that I've seen before include "this view is unacceptable" , "unorthodox beliefs" , "Unorthodoxy - apostasy" , "Unorthodox religious opinion" , "Iconoclasm" .)