Every year, Cressida spent the long summer holiday, and some of the spring, on the island. The house was lit by candle-light, and there was no electricity, telephone or television, so Cressida and the family lived like people in the olden days. In the evening, Cressida’s father told the children old Scottish tales about the people who lived on the islands round about, who were always fighting and tricking each other, and about dragons living in caves in the cliffs.
Cressida spent her time writing stories, fishing for things to eat, and exploring the island looking for these dragons.
These childhood experiences (quite apart from her fluency in Old Norse, of course), made her delighted to be approached to translate the Hiccup memoirs.
Excerpts of biography reproduced from http://www.howtotrainyourdragonbooks.com/about/