She left a devious ploy out (5)
I believe the answer is:
polly
'she' is the definition.
'left a devious ploy out' is the wordplay.
'left' becomes 'l' (common abbreviation).
'a devious' is an anagram indicator.
'out' is an insertion indicator.
'ploy' is an anagram of 'poly'.
'l' going within 'poly' is 'POLLY'.
(Other definitions for polly that I've seen before include "Parrot's name" , "Common name for a parrot" , "- - Toynbee, columnist" , "Fawlty Towers employee" , "Parrot; girl's name" .)