How Do I Forget or Delete An Available Device?

[WendySFO]

A week ago I linked to my friend's Heos sound system.  I will never need to do so again, but Heos still shows up all the time as an available device in my Spotify app.  I have tried signing out everywhere, but that did not get rid of this device.  I have tried deleting all offline devices, but since this device is "available", it is not offline and cannot be deleted.  

Can anyone help me solve this?  Do I need to call my friend and ask her to sign in on her own system?  That seems silly, plus she doesn't even use Spotify.

Advice would be greatly appreciated.  Thanks!