Spill the beans, when back, about her (6)
I believe the answer is:
stella
'her' is the definition.
'spill the beans when back about' is the wordplay.
'spill the beans' becomes 'tell' (I am not sure about this - if you are sure you should believe this answer much more).
'when' becomes 'as'.
'back' says the letters should be written in reverse.
'about' is an insertion indicator.
'as' backwards is 'sa'.
'tell' placed within 'sa' is 'STELLA'.
Can you help me to learn more?
(Other definitions for stella that I've seen before include "Swift alias for Esther" , "Paul McCartney's daughter" , "Swift favourite" , "girl!" , "woman" .)