My DD has the CF in a 29/18. Many of the girls on her 10U team swing some model year version of the CF. I think Demarini has figured out how to make light bats with pop for the younger girls.
Buy both, hit them and sell the one she doesn't like for a relatively small loss if you buy today. General thoughts seem to be that they are pretty similar in performance. One person prefers one over the other and vise versa. The prism will probably be slightly heavier (maybe 0.5oz).
Since they swing ghosts, if they perform well and are comfortable with them, then there's a chance they will not like the Demarinis. They are at opposite ends of the spectrum in swing weight. My DD currently uses a prism, previously a CF, tried the ghost and didn't like it.
Have someone that plays Div I softball, when she is home works with our kids and they are sponsored by Demarini and she told me that basically everyone swings the CF on their team.. So that is what I went with, I figured if it works for them it would work for her...