She was. Maybe it was past her bedtime? 
My guess (assuming that's she still big on tradition as she was in Luna Eclipsed) is that she probably didn't like being interrupted; that Twilight didn't show her and her sister proper respect or something trivial like that.
My guess (assuming that's she still big on tradition as she was in Luna Eclipsed) is that she probably didn't like being interrupted; that Twilight didn't show her and her sister proper respect or something trivial like that.