React badly to girl having a free hand (5,7)
I believe the answer is:
'having a free hand' is the definition.
(I've seen this before)
'react badly to girl' is the wordplay.
'badly' is an anagram indicator.
'to girl' becomes 'blanche' ().
'react' with letters rearranged gives 'carte'.
(Other definitions for carte blanche that I've seen before include "total freedom" , "Complete authority" , "Unrestricted authority" , "Full discretionary power" , "Free hand" .)