Yes, that's right. Definitely might be too extreme, but quite true, they will be a lot more prone to being discovered if she knew. I was just trying to say that I believe the main reason that Shinichi wouldn't let Ran know was not only that. Perhaps that is only 50% of the reason. If ever, his identity was being found out and chased by the BO one day, I believe he would still not tell Ran about it. He wouldn't want to endanger her life at any cost.
And I agree she can be pretty good at keeping quiet~ And keeping her mouth shut about secrets for that matter~ However, I think she's a person who is pretty easy to read. Not saying anything about something doesn't mean the other party wouldn't know about anything. I think, Okiya might already be suspecting something's wrong with the house... But he might not have linked his suspicions to Conan because he still knows nothing. If Ran continues to stay quiet, even if she was acting suspiciously, his suspicions wouldn't deal any damage.