**Possible SPOILERS** My version of this show's conclusion...
I know it's not, but if it were up to me, I would allow Rachel (Ran) to just figure out that Conan was, in fact, Jimmy Kudo.
Ya' know, maybe she'd have a few minor concerns/questions concerning Conan's actions, and decides to spend more time around him to find any cracks in his attempts to act like a six-year-old.
However, the "viewing audience" is left blind to her plan other than the fact that they'd notice she'd been spending less time pining over Jimmy, and more time hanging around Conan.
Maybe this would be better than an incredibly "cheesy" scene where Conan just reveals that he's always been living around Rachel. All the while, he's been solving her father's cases from behind the proverbial curtain.
In the end, wouldn't that just irritate her? The boy she's had a crush on has been secretly "spying" on her, and knocking out her father from time to time. That situation doesn't exactly scream romance...
If you think about it, the aforementioned ending might make more sense. The writers wouldn't be completely disregarding the fact that Rachel almost discovered his true identity in the first few episodes.
She is a detective's daughter, after all.
Leaving her clueless really wouldn't be fair (in my humble opinion, anyway)...