It would be kind of awkward for Nana to through all of that effort looking for Arika only to learn she was only a few blocks away from where she lived. I'm assuming this is just a starting point to retracing her steps or a red herring but leads to a chance encounter.
It's funny how Tanasaki is part of a conspiracy against Arika, who was willing to personally kill her, yet also knew they were finished without her help. Even after Arika disappeared, he still had to rely on that last connection to her to make Ruri and the rest of the group succeed.
With the truth out, even Yume now realize she how much of an impact Arika had on her.