Prepared Public Speaking is probably one of my favorite things in FFA. I started when I was a freshman, and actually just competed last thursday night and qualified for the state contest again.
I would say the way she delivers her speech is more important than the subject matter. But, I would challenge her to come up with it, because the judges will ask her questions and its alot easier to answer them well if she has background and passion for the subject.
Tell her to be confident and look the judges in the eye. Good luck!