This girl is getting mad at me for not reason?

Okay, so I play flute, and I used to be in concert band (the not so good band), and I just made symphonic (the good band) and I'm really happy because I even got first chair, but I knocked the first chair girl down to third, and the second chair one is still second. Anyway, we have to do this trio for a performance we are going to do, and I have to play first part, and I didn't practice it until we played it today. So the girl was like yelling at me if I got lost or accidentally missed a note! And she was like "Yeah, I've played your part more than you have." and she was being all snippy, why?