Any girl so mistreated might react thus (7)
I believe the answer is:
angrily
'thus' is the definition.
Both the answer and definition are adverbs. Perhaps you can see an association between them that I can't see?
'any girl so mistreated might react' is the wordplay.
'any girl' can be anagrammed to 'ANGRILY'.
But, I'm not clear how this is indicated.
Can you help me to learn more?
(Other definitions for angrily that I've seen before include "Crossly" , "In fury" , "in a temper" , "In irate fashion" , "in furious way" .)