THE solution is not to buy the wife an Android, that is ONE solution.
In total, there are a few solutions, I number them to make it easier to refer to them, not to order them from best to worst.
Get yourself an iPhone
Get your wife an Android
Wait for iOS 18
Switch to a messaging app like Element or Signal.
1 and 2: Unless you yourself can accept switching to using the other system, it is unfair to demand that the other part does that.
I have tried to switch to Android, I did it back in 2019, but I just disliked the feel of the OS enough that after dropping my phone and smashing the screen after 2-3 months, I didn’t even bother to get it fixed, I just moved back to my iPhone.
iOS 18 will have RCS, and will probably solve this.