Cannot add a contact to VIP list in the iOS Mail app

I was updating the VIPs in the iOS mail app today. I removed three contacts and noticed that my mother-in-law was not in the list, so I tried to add her. It seemed to add her successfully, but when it returned to the list, she was not there. I tried multiple times. I tried rebooting my phone. Based on and Apple Discussions forum post suggesting a workaround for issues when a suggested email is present in the contact card, I checked and there is no suggested email in her contact card, but her name and photo were set to autoupdate, so I temporarily disabled that and tried again, without success. I don't get any errors. Has anyone run into this issue before? Does anyone know a workaround or a fix? How can I add my mother-in-law to my VIPs. The contact card has 4 emails for her, a phone number, and all the basics. There are currently 9 VIP contacts.