So, I kept changing settings on the phone trying to get the text function working, and for other reasons, I deleted my wife's phone pairing and repaired it with MFT (I did this to change the name that MFT displayed for the phone, which I finally was able to find on her phone!).
Well, guess what works now without issue? The texting. We got into her car today and a text message popped up. That was a surprise! Then we sent one from my phone to her phone, and it worked fine again. I was even able to respond with one of the canned messages using voice commands.
One thing I found curious is that even though I renamed her phone, I had to delete it from MFT and re-pair it for the new name to appear. So that got me thinking... I had been changing settings on her phone left and right trying to get the texting working, but had not re-paired the phone. My conclusion, drawn from the fact that the texting now works after re-pairing the phone is this: MFT and the phone exchange settings only when the two are freshly paired and changes to the settings on the phone won't take effect until the two are re-paired.
Hope this might help some of those having issues. When I get the chance, I'll look at the settings on her phone and post them to see if it helps anybody else to get things working.
Also, since re-pairing, her contact photos now display in the phone book screen (before, only the caller ID photos worked). Go figure....