My contact shows up as "Other Devices" for AirDrop

Myself and wife both have iPhones. When I want to Airdrop a photo to her phone, I follow all the steps, including Bluetooth 'everyone in my contacts list'. Then I get a screen with her name plus another icon labelled 'other devices'.

If I select her name, Airdrop fails.

If I select 'other devices' Airdrop works and sends a photo to her phone.

I have looked on my phone and on my laptop for all the devices listed to me, and they are my iPhone, my iPad and my laptop.

Why is someone on my contacts list unavailable for Airdrop?

Why is their phone showing as one of my devices?

And how do I resolve this?

[Re-Titled by Moderator]

Original Title: A contact is listed as one of my other devices