A woman of that age probably doesn't pay due attention to wires and plugs or the general condition of the wiring in her van/annex. In this weather it could also have been inappropriate use of an electric heater. In any case, it pays to keep a regular eye on the safety of all electrical and gas fittings.
Some years ago we were in a caravan park in Bunbury and we were woken up at 3AM by thumping on the side of our van and shouts of Fire, Fire.
A caravan and fixed annex had gone up in flames while the owners were absent (believed to have be from an electrical fault with the fridge). The heat was so intense it melted the plastic type material of fake weatherboards on adjoining cabins, it just dripped like ice cream off the side of the homes. Luckily nobody was injured but the caravan and annex completely burnt out and several cabins damaged, but only to the outside walls.