Advent calendar day 23

While some runners have their breakthrough in high age, others do it early. The runner of today is maybe the youngest runner ever participating at WOC, when debuting in the relay at the age of 15. The runner is as far as I know the only runner born in the US that has won the World orienteering championships. But after a life in among others England, Denmark and New Zealand, the runner represented another nation than USA during the career. I want the first name of this runner that both took a medal in the birth country and the country the runner represented during the career.