Good Afternoon dcamdupe,
It looks like you're having a problem with using Home Sharing, so let's see if the following information can help with that.
As you're stating that your Mac isn't showing in the network, have you confirmed that it is connected to the internet and able to access the internet?
Once you've confirmed that, we'd recommend checking out the section labeled "Set up Home Sharing on Apple TV" of the following resource to see if this helps with recognizing and sharing information between your Mac and Apple TV.
Stream content with Home Sharing on Apple TV
We hope that's able to help.
Have a great day!