One person shows twice in Message App
On the MacOS Messages App, my wife shows up with two different message threads. Clicking on her name in each, one shows being associated with her phone number and the other is associated with her icloud.com email address. I have only one contact card for her in my Contacts app, in which I have both her email address and phone number.
Why is the Messages app maintaining two separate message threads for her? Is there any way to merge them into one thread and/or to force all of her devices (Mac, iPhone, IPad) to all use one or the other so that we don't have our message threads spread out in two different threads?