Woman's electronic key rejected (5)
I believe the answer is:
elsie
'woman's' is the definition.
'electronic key rejected' is the wordplay.
'electronic' becomes 'e' (as in e-mail or e-books).
'key' becomes 'isle' (I've seen this before).
'rejected' shows that the letters should be reversed in order.
'e'+'isle'='eisle'
'eisle' back-to-front is 'ELSIE'.
(Other definitions for elsie that I've seen before include "woman" , "Lady" , "Name for girl" , "Girl's name" , "Female name; rhymes with London football team" .)