I could be wrong, but I believe Garmin relies on the barometric altimeter for elevation tracking and gps for location, just like the Edge 305. The antenna is more sensitive and the software more sophisticated for faster satellite action.

http://www.gpsgenie.com/GPS-Garmin-GPSMAP-60CSx.htm

As far as accuracy of distance, she may have the 60csx set to record more frequently than you have your Forerunner -- in addition to the more sensitive antenna.