There's a few things that set the alarm bells ringing for me:
Firstly there is no verifiable data on the 53 marathons in 53 days challenge. Secondly, she failed to get independent observers for her 7 day treadmill WR attempt. Tertiary the biggest benefactors of donations made during the challenge(s) would of been the 53 foundation, which Amy and her partner are the trustees.
I'm not accusing anyone of anything however, the lack of transparency or sufficient monitoring around the two events (53 Marathons / 53 Days, 7 Day Treadmill WR) will undoubtedly lead many to speculate as to the validity and motives of the claims.