Stew has her way of using leftovers (6)
I believe the answer is:
rehash
'way of using leftovers' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'stew has her' is the wordplay.
'stew' is an anagram indicator.
'has'+'her'='hasher'
'hasher' with letters rearranged gives 'REHASH'.
Can you help me to learn more?
(Other definitions for rehash that I've seen before include "Rework old material" , "Use old material in a new form" , "Put old material into new form without much change" , "Recycled material" , "Same material, different mix" .)