Her first recorded professional competition was on November 6, 1999, when she completed the 8 km Senior Women's Cross-country race organised by the KAAA, where she finished 4th in a time of 34 minutes and 32 seconds.
On 25 Mar 2000, she won her first major competition at the 10 km KAAA Meeting tournament in Nyeri, in which she finished first with a time of 36:06.70, earning her a first opportunity to compete in an international platform in the United States.
[4] Between 15 April 2000 and 27 August 2000, Anastasia competed in 12 athletic competitions in the USA winning one of them and emerging second runner's up in a further three.
This was a 10-mile road race and her first major win internationally after she finished in first position in a time of 57 minutes and ten seconds.
On 9 September 2001, she was the third to finish the European Interclub Championships for Women race in Salò, Italy with a time of 51 minutes and 34 seconds.
A month later, in 22 Sep 2002, she won the Turin Half marathon with a time of 1:12:09, improving her personal best on the track from the previous year.
Her subsequent races in USA were in Dacenport, Falmouth, Flint, Park Forest, Philadelphia and Chicago between July and October.
Her final major race that year was back home in Kenya, in which she was number seven in the Nyeri half marathon in an undocumented time.
She further emerged second in two of them, the America's Finest City half marathon, at 1:16:01; and The Stone Harbor Lions Runwon none of them.
When she returned in 2010, Anastasia participated in the Standard Chartered Nairobi marathon in Nairobi, Kenya and the Standard Chartered Mumbai marathon in Mumbai, India in 2010 and 2011 respectively, she performed dismally in both races, taking the 12th and 13th positions with a time of more than 2 hours and 47 minutes in both.
She improved her time in the 2012 Nagano Olympic Commemorative marathon of 2012 when she clocked 2:43:33 and became the 9th athlete to finish the race.