Depends. Without knowing you or her but assuming she doesn't know how to guard it would be easy to land a cheap elbow in her face, which would pretty much end the fight. An elbow(watch videos in youtube to get an idea) is what Inexperienced people least expect (if she is way taller than you avoid face elbows). You could also try front kicking her knees or punch/kick/knee/elbow her ribs, eye grouches, neck and groin hits are game too. One last thing, if you get punched first you are done.

Without a PLETHORA of knowledge (your age, background, clothes you wear, etc.), it's going to be a wee bit hard to give you advise "on the fly".

I'd try to AVOID this sort of thing if at all possible--and that includes reporting her to whomever if necessary.

You might want to follow up over time with some self-defense lessons, however, as it could help you with confidence in general.

Ignor her

Go get a machine gun.

Someone at my school is gonna beat me up tomorrow. I never been in a fight before she has, but lost. And im not gonna fight her unless she punches me first. What are some tips to win ? Hurry pleasee !!