Having less she would be unsparing (4)
I believe the answer is:
ruth
'having less she would' is the definition.
I can't judge whether this defines the answer.
'be unsparing' is the wordplay.
'be' becomes 'rut' (rutting is a kind of being).
'unsparing' becomes 'h' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rut'+'h'='RUTH'
Can you help me to learn more?
(Other definitions for ruth that I've seen before include "Damsel" , "Girl's name and Old Testament Book" , "-- Rendell, novelist" , "Lady" , "distress once?" .)