I use this program for almost the same reasons you do (except I'm not married), and I hide the icon and set it to launch with Activator by double tapping on the Iphone status bar.
Now it is possible your wife could accidentally double tap on Iphone status bar, but I don't think that's a normal thing to do in iOS, it would have to be an accident. And you can set it to other actions (swiping up from bottom of screen, holding home button (way too likely to happen by accident IMO), etc.
If she ever finds out, you can use fake password feature, let her log in (nothing will be setup) and say you wanted to use it for the Whitelist feature but when you tried to import your contacts it said you must be registered and costs money. (if you try to add Addressbook whitelist from fake password version it will indeed tell you this).
The only feature I'd like them to update is this: while it is really cool that you can change the app icon, AND the app name, if someone was to open the app, it STILL says iBlacklist....so you almost get yourself in more trouble by faking an app name and she finds it, opens it and it says Iblacklist. I'd like it to also edit the app name that displays at launch, or maybe if someone puts in fake password set it to launch another app - for instance name it ESPN, and if fake password is entered it launches actual ESPN app and closes iblacklist. Then you could leave it in the open with fake name and fake icon.