On watching a little of the videos, of her running in a darkened shopping mall with nobody to chat to, I've become impressed with the effort she put in. She is supporting herself on the handles at times, which I presume is against the rules but those handles must be so tempting when you are dog tired. I see lots of runners leaning on those handles in gyms.
The simple math of 4 mph for 19 hours per day is where they went wrong. Laz will tell you that multi-day ultra running doesn't work like that. There is wear and tear and it's a difficult task to keep moving for that length of time. I'd say Dave did the maths and encouraged Amy that it would be no harder than sitting in a tub of baked beans as someone said earlier and that's how the challenge started. Then on the first day Amy only covered 60 miles and the math started looking shaky. There was too much invested in social media, sponsors etc to fail (think Skins and Rob Young) so the multiple quick 10k efforts happened late in the week.