Another difference not stated here is the fast-charging capability on the new MBA, 50% in 30 minutes, depending on your gf's lifestyle this might be relevant, a former gf used to be permanently on the run, always having to pack the adapter, which was messy, the magsafe cord ended broken etc.
With the great battery-life of AS Macs and the flexibility of usb c as a fallback charging option, she might be able to fast-charge and run without having to bring the adapter along for the day, etc. Like charging your Apple Watch before going out.