Error trying to share Airtag saying both devices need to be on latest software

We have an Airtag in my daughter's school backpack (she just started kindergarten) so we can see when she's on the bus home. I set it up a couple of days ago. When I try to share that Airtag with my wife's AppleID account, the Find My app says:

-------@gmail.com is not eligible for sharing.

Sharing with this person requires the latest software on both of your devices. It can take up to a day after upgrading for sharing to become available.

I had her update her M2 MacBook air to the latest version of Sonoma. I am also on the latest version of Sonoma (14.6.1).

When I try to add her by phone number, it returns:

This phone number does not appear to be associated with an active iCloud account.

I know for a fact that this is 100% not true because I had to help reset her iCloud account a few weeks ago and personally made sure all the profile information was complete (mostly because I don't want to have to do it again).

I'm following the instructions in this article: Share an AirTag or other item in Find My on Mac - Apple Support

Why can't I share the Airtag based on either of the profile attributes which I know for a fact are accurate?