I totally agree with Vaughan!
It could be a your wife’s provider issue.
Try to send yourself some test MMS, especially now that you are using a different SMS/MMS client, or at least ask to someone to do it.
For example, here in Italy mms is no longer used by anyone because everyone uses whatsapp to send photos or videos, and often many people don’t even have the active configuration to receive them on their smartphone… and then it costs a lot!
(By the way, I remember that years ago, I had a lot of problems with send/receive mms, but it was in the 2g/3g world only :-D. )