Looking at the challenge and available footage I’m pretty confident that she did the 7 days in the challenge (that is to say she was present and running n the treadmill). The issue for me is that without truly independent monitoring it’s hard to verify that she covered the miles claimed.
Running 521 miles in 7 days requires the athlete to run over 74 miles per day for 7 days. Whilst that *may* sound easy to some let me tell you, as a qualified Endurance Coach I can assure you that a run like that is beyond most runners. Indeed, when you look at the world record you’ll see that Sharon Gayter (GB Athlete) hasn’t managed that and, a well know ultra runner named Dan Lawson (also a GB Athlete) managed to run the same distance (521 miles) in the same time frame (7 days).
I’m not saying it isn’t possible however, looking at the known results for Amy it seems unlikely that someone who’s ran a small sprinkling of 4 hour marathons and has an official marathon PB of 3.53 is capable of breaking a world record that several known international standard ultra runners were unable to beat. If she truly in that class of runners then I would love to see her running some 50 or 100K races and wearing a GB vest.