A strain working for emperor’s wife (7)
I believe the answer is:
tsarina
'emperor's wife' is the definition.
(I've seen this in another clue)
'a strain working' is the wordplay.
'working' indicates anagramming the letters.
'a'+'strain'='astrain'
'astrain' anagrammed gives 'TSARINA'.
'for' acts as a link.
(Other definitions for tsarina that I've seen before include "Consort" , "Russian empress (S, not Z)" , "Nicholas's wife" , "titled lady" , "Monarch" .)