That will work, assuming you don't have some other audio playing loudly so she can hear you. The steering wheel button mutes other audio so she can hear me and I can hear her.You're right. Probably should have mentioned that. 6S added ability to do it without being plugged into power. 6 can do it as well but has to be plugged in.
I was traveling and had a rented Hundai last week. Plug in my phone and immediate access to all my music. Why not my $100K Telsa? Even with all my music on a dedicated USB stick, my Tesla still can't understand playlists.