Everything Evita changed, her heart to soften (9)
I believe the answer is:
alleviate
'soften' is the definition.
(thesaurus)
'everything evita changed her heart' is the wordplay.
'everything' becomes 'all' (all things).
'changed' is an anagram indicator.
'heart' means to look at the middle letters.
The centre of 'her' is 'e'.
'evita' anagrammed gives 'eviat'.
'all'+'eviat'+'e'='ALLEVIATE'
'to' acts as a link.
(Other definitions for alleviate that I've seen before include "dull" , "Make better" , "moderate" , "Make (pain) less intense" , "Make light" .)