Watch the video and you will see the truth.  Her camp went into spin mode, saying it was the first time Ashlee ever used a "backing track".  And her band played the wrong song.  And she had acid reflux.  Do they think we are idiots?  Do they think it is some kind of industry secret that singers lip sync all the time?  Hell, I'm more surprised when someone DOESN'T lip sync.
Check out her flub