Steve,
If I had to guess I would assume that your wife's iPhone has the incorrect password information stored for the MiFi. You are going to have to try to re-enter that information on the iPhone to correct the problem. I do not have access to an iPhone so I wont be able to provide you with the specific steps to accomplish that goal. A quick google search or a call to apple may be the best course of action there.
What I can help you with is looking up your password credentials and configuration information. Once you know that setting up a connection on your wifes device should be much easier.
To look up password info on the MiFi 4620L:
1. Power up and connect to the MiFi on a regular computer
2. Navigate to http://vz.hotspot
3. Log into the MiFi with your admin password (default is posted to the back of the device)
4. Navigate to WiFi > WiFi Profile
5. Record the following information
a. Network Name (SSID)
b. Security
c. WiFi Password
Once you have this info then try to re-enter it on the other iPhone. Perhaps something was entered incorrectly the first time around. The stats above should contain all the info that you need to create a good connection.
If these steps do not help the next thing to try would be switching the 802.11 mode. I believe the default is B+G, so try bumping it up to B+G+N. You can also try ruling out WiFi passwords all togeather by switching the selected profile type from secured to Open. I do not recommend leaving your MiFi as an open connection, but sometimes it's helpful for troubleshooting purposes to know if the devices are incompatible or not.
