I just got my new Lumia 1020 which runs Windows Phone 8, and wanted to set up my Google stuff to sync with the phone. I use two factor auth, and after creating an application specific password, it synced up all my email, and my own calendars.
But my wife’s shared calendar did not show up, and given the history of issues between google and Windows Phone, I started searching for a solution. The Lumia 1020 is no longer using Active Sync, so all the old guides were no longer relevant. By pure luck, I stumbled on a post with this link:
That will let you select which calendars should be synced when using CalDAV access, which is what the Lumia 1020 is now using.
You might need to remove/save/add the checkbox for syncing calendars for your google account on your phone before it shows up, but I now have the shared calendar in there as well.
I hope this might help out others struggling with this.