As a singer and a performer she should know her limitations better. There are plenty of people with worse vocals than her that have better reputations(granted not as famous) because they sing within their means. I appreciate the effort and I like that she is brave enough to sing live.
Doing too much, Katy! So sad. This song is so good too.
Honestly, I feel like I've heard her hit those notes before in other performances. If girl had just chilled out instead of spinning around in the air it may have been less of a mess. After seeing this though, I have decided that I can sing the chorus better.
You have such an amazing voice. I don't know why you always want to be different. 
You should've done an acoustic version of the song.
Doing too much, Katy! So sad. This song is so good too.