She's evasive about having one left (5)
I believe the answer is:
sally
'she's' is the definition.
'evasive about having one left' is the wordplay.
'evasive' becomes 'sly' (I've seen this in another clue).
'about' indicates putting letters inside.
'having one left' becomes 'al' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sly' enclosing 'al' is 'SALLY'.
Can you help me to learn more?
(Other definitions for sally that I've seen before include "Sortie; quip" , "- - Lunn, flat cake" , "Sarah might make a witty remark about the willow" , "Charge" , "army" .)