Face timing my friend only connects on her iPhone, not her Mac

When I initiate a FaceTime on my Mac to my friend, it only registers on her iPhone, not her Mac. Likewise, when she initiates a FaceTime on her Mac to me, it only comes in on my iPhone, not my Mac. We can't get a Mac to Mac FaceTime, and can't figure out why. My Mac and iPhone FaceTime preferences both state I can be reached at my phone #, my iCloud email, and my Apple ID email so there doesn't seem to be any reason why both my computer *and* iPhone wouldn't register an incoming FaceTime to *everything* someone could call me at. I've spent an hour Googling and haven't found anything related to this. Does anyone have any ideas?

Her Mac runs Mavericks, while mine runs Yosemite (though this was a problem before I upgraded too). My iPhone is iOS 8; hers is probably 7.