Yamauchi was born in Oxford, Oxfordshire, England to Dorothy and Norman Myers, and lived with her family until she was eight years old in Nairobi, Kenya.

In 2005, she ran her second marathon (2:31:52) at London, earning selection for the 2005 World Championships in Athletics in Helsinki, Finland, where she finished 18th and won a team bronze medal.

In December 2005 she was selected for GB's support scheme for elite athletes, the Lottery-funded UK Sport World Class Performance Programme.

In January 2006 she took unpaid leave from the FCO to focus on preparing for the 2008 Beijing Olympic marathon, and moved to Tokyo, Japan with her husband.

At the 2008 Summer Olympics in Beijing, Yamauchi equalled the best performance by a British woman in the marathon by finishing sixth in a time of 2 hrs 27 mins 29 secs.

She suffered a foot injury after this and was eventually forced to withdraw from the 2009 World Championships in Athletics in September, missing out on a medal chance in the marathon race.

[5] Having fully recovered, she scored a prominent win at the 2010 New York City Half Marathon, seeing off competition from Deena Kastor to cross the finish line in 1:09:25 – an 18-second improvement on the course record.

[11] However a foot injury forced Radcliffe to withdraw and Yamauchi failed to complete the race, dropping out after six miles with a bruised heel.