I mean, it genuinely doesn’t matter in the long term.
Graduate programs don’t care whether or not you got credit for doing research as long as you’ve done some research. I never got actual course credit for any of the research I did as an undergraduate. That’s not really important; what’s important is actually doing the research and getting the training and experience.
So, if she decides to take the AP research credit, that’s not going to affect her graduate applications. If she doesn’t take it, that also won’t affect her graduate applications. The fact that she got a perfect score doesn’t really matter; I’d be willing to bet good money that no graduate professor is really going to care that much about it (in fact I’d be surprised if more than 20% even know there IS an AP research class and how it’s scored). And the score doesn’t show up on the transcript anyway.