Let me restate my question as a statement.
On my home network (wired and wireless mix), I can see every host, Windows or Mac, that has file sharing enabled. I can also see every Mac that has Screen Sharing enabled.
That means I can see some of my macs, and not others, because those others (the kids laptops) do not have File Sharing enabled.
If you cannot see her on the same network, either she's running a firewall or she's not enabled any sharing, or both.