Well, it most likely is. But even just Japan is not exactly that small of a place. Maybe her old family are in one end of the country and her new one is in the other. Potential for some time to have passed between her death and rebirth, too. Lot of factors. If this wasn't a manga I'd say running into them has way lower odds than she'd probably like. Since it is one, well. The author either wants to have her run into them or not.
Sand castle....even now...I doubt I'd ever make that kind of a sand castle with nothing but sand and my hands XDDD Even the other girl managed to make quite an incredible sand castle o.o