I still can't figure out if her vocals are good or not
That probably means you don't like her vocals haha ... while no one will ever mistaken her for Adele, she's def. a very capable singer. There are many other pop singers that are far worse than she is.
After re-watching the vid, I think she was miming some parts.
Nawp she wasnt, the backing vocals were TOO MUCH LOUD! but the performance was great overall!! it wasnt boring, it made everybody on the crowd wanna jump and ****! and that is the most important thing, i hope the song get back to #1 asap!