OP, more info is needed. Is it all the time that you and the wife can’t text, or only while she is driving? Do other people texting your wife have the same problem? Has she tried restarting her phone?
For those people with other types of phones, Apple recently released a major update to the operating system for the iPhone called iOS 11. It includes a feature called Do Not Disturb While Driving. Incoming messages are muted and the phone sends out a message that you are driving. People are informed how to get through in an emergency. Passengers can turn off the feature by pressing “I’m not driving.” Do Not Disturb While Driving can also be disabled. Personally I think it’s a great feature.