How to uncouple two Iphones sharing the same Icloud account without deleting BOTH?

I purchased a new Iphone 14 pro max to replace my Iphone 11. I have an Icloud account and used it to copy all my Iphone 11 content to the new Iphone 14. All is good; the 14 is set up and working good. then my wife decides she wants to take over my old 11 to replace her old flip phone.

So I took the Iphone 11 and her flip phone to the Verizon store and have them to move her flip-phone number over to the iphone 11 (they replaced the sim card). She had no flip-phone data to transfer. But all of the contents that was on my Iphone 11 remained on it.

Now I have two phones with different numbers with exactly the same content; I need to customize her contents, but every change I make on her phone changes mine also (both phones log into the same Icloud account.

Do I have to discontinue the Icloud account, then delete the Apple id on her phone and get a new Icloud account and set up a Family Share?