She is trained by Bob Kersee, husband of Jackie Joyner-Kersee, six time Olympic medalist also from her hometown of East St. Louis, Illinois.

Her sophomore year was met with much adversity when she tore her posterior cruciate ligament (PCL) and meniscus before the IHSA sectional meet.

She received All-American honours twice at the 2004 NCAA Women's Outdoor Track and Field Championship, after coming eighth in the 100 m hurdles final and taking second place in the 4×100-meter relay.

During training for the 2008 Beijing Olympics, she struggled with getting sponsors, but was given a hand by her teammate, injured hurdler Michelle Perry, when she was given a pair of spikes.

[5] It was a surprise win amid crushing losses to US Olympic track-and-field team favorites, Lolo Jones and Sanya Richards, and propelling Harper to international renown.

With four months of training, Harper again made the US team placing third in the 100 meter hurdles at the USA Outdoor Championships.

As she raced to prepare for the 2012 Olympics in London, Harper traveled to the West Indies to start her season with a victory at a rainy Guadalupe Meet.

She then crossed the Atlantic to win both the Rome Diamond League 100m hurdle showdown and the Colorful Daegu Pre Championship Meet in South Korea.

[8] In London, Harper showed great fitness advancing from the quarterfinals in 12.75, then a running a season's best and personal record 12.46 in the semifinals.

[9] After the London Games, Harper continued the Diamond League tour finishing the second half of her season undefeated.

Next she traveled to Lausanne, Switzerland to post the second fastest time of her career, 12.43, at the Athletissima Diamond League Meet.

She ended her May competition in Manchester, England by winning the Great City Games Street Race then traveling to Rome, Italy, Harper-Nelson to capture her 4th total and 3rd consecutive Golden Gala Diamond League victory.

Harper-Nelson left Iowa for the Sainsbury's Grand Prix Diamond League in Birmingham, England, which she won in a time of 12.64.

Nelson regrouped and set out to finish her Diamond League tour first stopping in Croatia to beat a similar field to the Moscow World Championships featuring Sally Pearson.

[18] The Diamond League race was once again a huge hurdle, but winning Birmingham and running a World Lead 12.44 at Stade de Paris,[19] brought the competition down to the wire at Zurich.

She celebrated in effervescent fashion, and delighted the crowd on the first bend, by turning cartwheels on the track beyond the finish line.

[20] " Winning her 3rd consecutive Diamond Trophy, Harper-Nelson went to represent the Americas at the IAAF 2014 Continental Cup in Marrakech, Morocco.

In spite, Harper-Nelson dusted herself off and won her 4th Diamond League title at the IAAF Brussels Diamond League Final[23] Though she did not qualify for the 2016 Rio de Janeiro Olympics missing the qualifying time by .01 seconds, Harper-Nelson remained positive saying she was “grateful” for her amazing career.

Following her silver medal in the London Olympics, Harper-Nelson was named the new Ambassador for United Way of Greater St. Louis Education Express.

The proclamation was passed by Illinois governor Rod R. Blagojevich, and was celebrated with a parade and a public gathering in Harper's hometown of East St.

Before the London Games, she came in first place in the US Track and Field Trials held in Eugene, Oregon, despite soggy conditions.