Curious about this. Have you tried both logging in at the same time, what happens? I assume you're both connecting from the same network right? Was reading that it might be possible but that's just via some basic searching. It looks like it's still considered 'sharing' and isn't allowed by the rules but not sure if they're enforced.
If she logs in on her device it logs me out :( i just made a new BNET account and transfered my WoW character over (25 bucks!) luckily I hadnt bought shadowlands yet.