Her speed on the treadmill could be estimated by counting the number of times the word "Sole" appears on the end of the treadmill belt over a defined period of time if the size (length) of the belt is known.
The Sole treadmill has an automated self calibration sequence. I wonder if they calibrated the machine every day?
None of that even matters anymore.
Just watch the parts of the video that Scam_Watcheroo highlighted.