She twice left little Beatrice out (5)
I believe the answer is:
bella
'she' is the definition.
'twice left little beatrice out' is the wordplay.
'twice' shows that letters should be duplicated.
'left little' becomes 'l' (abbreviation for little. I am not sure about the 'left' bit.).
'beatrice' becomes 'Bea' (Bea is short for Beatrice).
'out' is an insertion indicator.
'l' duplicated is 'll'.
'll' inserted inside 'bea' is 'BELLA'.
Can you help me to learn more?
(Other definitions for bella that I've seen before include "Girl" , "Girl's name" , "Deadly nightshade or atropine" .)