She did not compete collegiately in 2010 and turned professional instead. She won the 100 m at the Mt. SAC Relays in April and ran the 200 m at the adidas Grand Prix in New York in June. At the USA Outdoor Championships she reached the 200 m but finished last. Williams ran on the 2011 Diamond League circuit, including a runner-up finish in Doha. She ran a best of 52.71 seconds for the 400-meter dash in March, but did not perform well at the U.S. Championships, being eliminated in the semi-finals. Williams had a number of good performances in Europe in 2012, including a win at the FBK Games, podium placings at the Bislett Games and Meeting Areva, then a win at the London Grand Prix. She did not gain a place on the Olympic team, however, as she failed to reach the 200 m final at the 2012 United States Olympic Trials.