The reasoning Nine has held for her actions throughout CF have been pretty flimsy in general, especially when compared to her past self. I know there's a degree of corruption involved but by now I really can't see it as anything but just silly. I honestly would not be surprised if they broke down her plans by just having Celica tell her this since it seems difficult to tie up her plotline otherwise.
If she had been the final antagonist which I had anticipated then things would be a bit different, but right now it seems like they're going to have to rush for closure, and what better way to do it than Ragna proving himself once again before her? I can think of a couple of things, but I doubt they want to stretch that part out as much as one would expect, seeing as how they're pulling Es out of nowhere now and building up Nu alot.