She attended Thomas Worthington High School, setting school records in the 200 meters and 400 meters as a freshman. In her sophomore and junior years she concentrated on soccer, dropping track and field
She returned to the track in her senior year, but soccer remained her main sport, and after graduating from high school she went to Indiana University on a soccer scholarship. She played soccer through her freshman year at Indiana, but knee problems, which she had already suffered from in high school, forced her to drop soccer and give up her scholarship. Track was not a problem for her knees, so she joined the Indiana Hoosiers" track and field team in her sophomore year, now running the 400 meters and 800 meters, and earned a new scholarship through that sport.
The 800 meters soon became her main event, and she developed steadily.
At the 2010 National Collegiate Athletic Association championships she placed second to Phoebe Wright in a personal best 2:02.14. Later that summer, she broke two minutes for the first time, running 1:59.83 in Lignano.
Sponsored by the shoe company Saucony, she turned professional. She continued to train under her coach at Indiana, Ron Helmer.
In 2011, her first full year as a professional, she improved her personal best to 1:59.12 (again in Lignano) and placed seventh at the United States championships.
In 2012 she placed second behind Fantu Magiso at the Adidas Grand Prix, running 1:59.18. She narrowly missed qualifying for the 2012 Summer Olympics. At the Olympic Trials she was in the top three until the end, but tied up and fell to fourth place with meters to go.
She returned to the track in 2014, placing third at the United States championships.
She finished in the top six in four Diamond League meetings, breaking two minutes in both Lausanne and Monaco. Track & Field News ranked her #10 in the world that year, her first top 10 world ranking.
She placed fourth at the United States championships in 2:00.09, missing qualifying for the World Championships in Beijing by 0.04 seconds. The following week she improved her personal best to 1:58.68 at the Paris Diamond League meeting, where she also placed fourth.
After Ajee" Wilson withdrew from the World Championships due to an injury, Ludlow was named as her replacement.