Trying to program it anyway results in an error like
avrdude: Error: Could not find USBtiny device (0x1781/0xc9f)
The issue seems to be somewhat intermittent, too. Occasionally it works on her Macbook Air. It always works 100% of the time on my Lenovo T460 (Linux). So there's something platform related...
Not a great intro. The Gemma doesn't behave like usual Ardiuno systems - it doesn't expose a USB serial port, for example - so answers are also thinner on the ground.
But I think we found something.