I've received the answer to my message from the poster. Here her mail:
"Yes, other people have wondered, too. And have wondered rather rudely which is why I disabled the comments. I got the video from her site way back when she wasn't as huge of a super star (we're talking 2000 to 1999) when she had an actual biography up that she had written herself and in it she explained that she was trained classical piano and would often go to radio shows and play pieces for them and that's where I got the video from. Of course I can't provide a link now, because her site is completely redone and all of that stuff is lost. But I don't understand why you don't think it's her. I understand the video is of bad quality, but did you just not know she could play piano like that, or did you not know she looked like that under all of her make up when she was younger?"
So it really seems that IT'S HER! Sooo talented!