Being somewhat diplomatic, I would say that it was here mental determination coupled with her rather large stature that did the "trick".

I remember when I was a kid hearing about an Icelandic guy, Guðlaugur Friðþórsson, who spent 6 hours in freezing icelandic waters and survived. He was also quite large.

http://www.vikingrune.com/2009/03/true-viking-grit/