fourth year
From your description, and without seeing the actual installation, it appears that you can either install a “Y” on its side or a combination Y-1/8 bend on its back. Since it appears to be a single story you should not have to worry about a pressure zone when you make the connection to the horizontal pipe, and since the original pipe appears to be vented and you are venting this one also, they should be no “wet vent” situation. But, one thing that drives me “up a wall”, and also did when I was a supervisor, is to tell someone how I wanted it done and then find out that they did it differently.
