I wouldn't mind at all if my best friend got the same bag as me. Actually, I would be happy, because it would enhance the sisterly feeling between us.
I recommend that instead of feeling annoyed, perhaps you can think of this situation in a more positive light--your friend admires your sense of style.
I recommend that instead of feeling annoyed, perhaps you can think of this situation in a more positive light--your friend admires your sense of style.