In one of her old posts (I can remember if it was a live or facebook post) she stated that the way she learns the songs is by selecting portions of the song and playing along them until she gets them perfect, then adding the next part (something like 20 sec at a time) until she completes the entire song, she then plays along the track multiple times until she has completed the song with all perfect takes ( therefore there are NO mistakes in her videos). I have seen a very old video of her playing Judith ( A perfect circle) where her friend Jenn is holding the camera so there are no extra takes and no extra cameras, and she does play the entire song correctly note for note. Anybody can learn most music that way which is why you see 9 year olds nailing hard stuff... When you can correct mistakes via editing, then anybody can play perfect.
All that said, she has played some hard parts and played them correctly. Even if she was just faking it, you have to know what you are doing to look that convincing. Now those that say someone is the best are biased by how well known or popular someone may be (all those Peart fans out there) is he the best? not IMO but he was great at what he did, to me the best drummer is like the most beautiful girl.. what I like is going to be different from what others like so it's on the eye of the beholder...
Whether she can play a full song on camera in one take or not doesn't prove her worth, she can still nail those sections at the end of the day.