It may be a strain for a Russian empress (7)
I believe the answer is:
tsarina
'russian empress' is the definition.
(I've seen this before)
'it may be a strain for a' is the wordplay.
'it may be' indicates an anagram (I've seen this in other clues).
'for' says to put letters next to each other.
'strain' with letters rearranged gives 'tsarin'.
'tsarin'+'a'='TSARINA'
(Other definitions for tsarina that I've seen before include "Russian noblewoman" , "Wife of a tsar" , "Monarch" , "Wife of royal Russian" , "Russian royal; Sinatra (anag.)" .)