Chirpy redhead devastated by such a victory, perhaps (7)
I believe the answer is:
pyrrhic
'such a victory perhaps' is the definition.
(as in the phrase pyrrhic victory)
'chirpy redhead devastated' is the wordplay.
'redhead' becomes 'r' (head letter of 'red').
'devastated' is an anagram indicator (devastate literally means destroy or lay waste to).
'chirpy'+'r'='chirpyr'
'chirpyr' with letters rearranged gives 'PYRRHIC'.
'by' is the link.
(Other definitions for pyrrhic that I've seen before include "A victory won at such great cost that it's not a triumph" , "This kind of victory is too costly" , "This victory comes at too great a price" , "A victory won at too great a cost to the victor" , "Such a victory as bad as defeat" .)