Declare Vera to be at fault (4)
I believe the answer is:
aver
'declare' is the definition.
(averring is a kind of declaring)
'vera to be at fault' is the wordplay.
'to be at fault' indicates an anagram.
'vera' is an anagram of 'AVER'.
(Other definitions for aver that I've seen before include "State firmly, propound" , "Firmly maintain" , "State firmly, maybe rave" , "State; say" , "Declare or insist" .)