Hey David Fritzinger,
We understand that your wife isn't able to receive messages through her phone number on her iPad. To confirm, is text message forwarding enabled on both your wife's iPhone and iPad? If unsure, check out the details below which show how to check and, if needed, set it up:
"Set up text message forwarding
- On your iPhone, iPad, or iPod touch, go to Settings > Messages > Send & Receive. On your Mac, open Messages, choose Messages > Preferences, then click iMessage. Make sure that you're signed in to iMessage with the same Apple ID on all your devices.
- On your iPhone, go to Settings > Messages > Text Message Forwarding.*
- Choose which devices can send and receive text messages from your iPhone. If you're not using two-factor authentication for your Apple ID, a verification code appears on each of your other devices: enter that code on your iPhone.
As long as your iPhone is turned on and connected to Wi-Fi or a cellular network, new SMS/MMS texts can be sent and received on the devices that you added."
The information above is from this article: How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac Ensuring that is enabled should let your wife be able to use SMS/MMS on her iPad as well. It is also possible that if your wife's phone number isn't showing in Settings > Messages > Send & Receive, she may need to turn off iMessage and try activating it again with the same Apple ID she uses with her iPhone: Set up Messages on iPad
Let us know how that goes. Take care!