"Like I said, Kagari looks like Kurisu because of the deja vu effect. It's not nothing..." Is what you said. I might have misinterpreted it but it sounded like that's what you were saying. With that mixup out of the way, I've really been trying to figure this out, so I've gathered the most popular theories here-
-Kagari is Okabe and Kurisu's child (Disproven)
-Kagari is a clone of Kurisu (Possibility)
-Kagari is just another regular person (Possibility)
-Kagari is Kurisu (Disproven)
Like I've been saying this entire time, we don't know her real family name. It would seem like lazy writing if at the end her appearance was mere coincidence. (Plus, red hair in Japan is crazy rare anyway). Even though the process is long and convuluted, SHE COULD be a clone of Kurisu. At the moment this seems like the most logical theory, but that's only until I think up a better one... She could also just be another World War III orphan, but the amount of coincidences there just seems a bit impossible.
I have another theory, but I need to ask a question first: Would Kagari exist on other attractor fields besides Beta? The answer will determine the validity of my theory.