Calendar event Invitee is a non-existent contact

When I create a Calendar event on my iPhone and click Invitees, the default name that displays is not one of my contacts. How is this possible and how can I get rid of it and replace it with a real contact record?

The rogue contact that displays is my wife's nickname that my brother-in-law uses and her email address. It's shown up as my default Invitee ever since my brother-in-law invited us to an event a few months ago. I've tried deleting her contact record and re-adding it, but that didn't help. Then I tried deleting her contact record again and adding it via iCloud, but that didn't work either. I also tried removing all the calendars, shutting down, and re-adding them, and that didn't work either. I don't know what else to try and would love some advice.

I have a new iPhone SE (bought in November 2020) iOS 15.1.