this happens to me with Sprint if my phone is off at the time the message is sent.
The key to remember is that SMS (Short Message Service) is not an instant message service, and never has been. Likely if you dig around your carrier you will discover that most don’t guarantee instant delivery.
Things that will delay an SMS can include:
The message was sent on another carrier, and is de-prioritised by outgoing traffic - SMS will always be de-prioritised by voice calls, backhaul, and other traffice
Your phone is off, not charged, under charged or otherwise compromised
The location of the sender, or the location of the recipient (and the resultant backhaul through carriers
Being sent on cell/mobile tower borders, in/around tall buildings, mountainous regions, etc. with spotty coverage
SMS is really just a way that telco monetises the data packets that are sent between phone and tower anyway. It is reliable but not a priority to deliver, like voice or data. Better to use an instant message service.
I can’t explain 5 weeks though. That’s just weird.
Same carrier, same phone plan, distance 5 miles, both phones on and charged and updated to same OS.
A week and a half.
Does this problem exist when you text people other than your wife? What sort of phone does she have? Does she have this problem with delays, when she texts people?