I feel bad for the girl. Many fans would think it's a chance of a lifetime to get an autograph at that time when there's no one else but she got shut down BADLY.
This woman is harassed anywhere she goes, give her a break. I'm sure a lot of the people saying she's rude would do much worse to a fan after years and years of the same ****. We've become accustomed to pop stars "owing us" their time off the stage but they DON'T. They're real people and if they don't want to sign your ****ing autograph they don't have to. Their job is to entertain in videos and in concert, they don't have to do anything else for you.
I get that she was in a hurry but it wouldn't have taken any longer to sign that paper than telling the girl no.