Re: Very disappointed with the Zenfone 2
Is your wife's phone running 5.0 or a Kitkat version? I don't have a Zenfone yet to see if Asus has made any changes to the default Lollipop behavior, but in Android 5.0, "do not disturb" was replaced with "Interruptions." This no longer allows you to set a specific group to exclude or allow. However, you can use your Favorite Contact list as a group to allow. So, the only workaround is to configure your Favorite Contacts as exactly the people you want to allow to be able to contact you in this mode.
You can set your Favorite Contacts to be allowed in settings under Interrruptions, which is under Display settings - Sounds and Notification. You will see a line that says "Allowed Contacts" and you can choose it there. Again, I don't have a Zenfone, so these are general 5.0 settings and I don't know yet if Asus has changed anything. But it's possible your wife's phone was not yet on lollipop OS when you saw the old style Do Not Disturb feature.
There are several Do Not Disturb apps in the Play Store which you can try out as well. I haven't used any of them so will not make a recommendation, but some have good ratings. So do a search there.