That's unlikely, first because she hadn't met the actual Shiho before. Ran might think Ai thinks maturely for her age but that'sonly it. Besides, there are really some kids who act that way. Ran only assumed Conan and Shinichi are the same because she is already familiar of the latter's habits. And as far as the story goes, Ran confronted Conan of meddling with Agasa's experiment causing him to shrunk, only to give an excuse right in time. So, Ai as the shrunken version of someone else? No.