Hmm...well, I kind of ruled out C, since when she switches the key, I think the aim is to make the vocals lower...and from the video, it seemed like she was playing both black and white keys, so that would rule out C as well...of course, if I'm wrong about that, I could understand her playing it in C there since there's a band there...if that's what key they all learned it in or something, then she would have to accomodate for them rather than herself...