iPhone suddenly adds "11" when I message my wife

I've been texting my wife's number from this phone for months. Suddenly today I am getting an error message telling me I need to use a ten digit number. The number the error thinks I'm trying is my wife's number but with "11" added to the beginning.

So far I can still text other people without the error.

A similar error error has been reported before. One of the suggested fixes is deleting and recreating the contact and deleting all the texts, but I'd really like to avoid that if I can. I don't want to lose all of those texts.

I tried removing the "1" from the My Phone Number setting, turning MMS off and on, turning off dial assist, turning the phone on and off, manually deleting just her number and entering manually in a text message, and none of that has worked.