Shirt over Hindu garment upset an empress (7)
I believe the answer is:
tsarina
'empress' is the definition.
(I know that tsarina is a type of empress)
'shirt over hindu garment upset an' is the wordplay.
'shirt' becomes 't' (as in a T-shirt).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'hindu garment' becomes 'sari' (I've seen this before).
'upset' shows that the letters should be reversed in order.
'an' backwards is 'na'.
't'+'sari'+'na'='TSARINA'
(Other definitions for tsarina that I've seen before include "Consort" , "lady of some importance" , "queen" , "Nicholas's wife" , "titled lady" .)