Trains a new empress (7)
I believe the answer is:
tsarina
'empress' is the definition.
(I know that tsarina is a type of empress)
'trains a new' is the wordplay.
'new' indicates anagramming the letters.
'trains'+'a'='trainsa'
'trainsa' is an anagram of 'TSARINA'.
(Other definitions for tsarina that I've seen before include "Wife of an old Russian emperor" , "Wife of a tsar" , "Foreign ruler" , "Russian noblewoman" , "companion of emperor" .)