Why shouldn't she be criticised? Of course people are always going to be critical, as a "celebritie" she is, she has to take it. If you put yourself to that level of exposure, deal with it and be prepared to be criticised.
I don't think her performance was good, we all know she isn't the greatest singer and i didn't like the outfit either .Don't get me wrong, i don't hate this girl but, i don't like her either.