Try restoring the phone software through iTunes.
First, plug the cable into the iPhone and to a computer. If you do not already back it up using iCloud, then use iTunes to back it up (right-click the name of your phone in the left side bar of iTunes, hit "Backup"). Then hit the Restore button in the main iPhone page of iTunes. This will download the operating system, wipe the phone, and install a fresh copy of iOS, which usually solves random software glitches. After it is done installing, it will then ask if you want to restore from a backup of your phone. You'd do that then, and it will put your settings and apps back into place.
Regarding the wifi connection, is your router a dual-band 2.4ghz + 5.0ghz router? If so, then you'll need to make sure that the 5.0ghz band has a separate name (SSID), because the iPhone can only connect to a 2.4ghz wifi network. If your router is broadcasting on the same name on both 2.4ghz and 5.0ghz, that may cause a problem with iPhone 4S trying to connect to it. (If your wife's phone is an iPhone 4 or also a 4S, this is probably not the issue, though)