In the 2004–05 season, she qualified for the 2005 U.S. Championships on the senior level and placed 10th. Because of that placement, she was given a Junior Grand Prix assignment the following season.
In the 2006–07 season, having aged out of Juniors, Williams-Stewart was no longer eligible to compete on the Junior Grand Prix. She was sent to the 2006 Ondrej Nepela Memorial, a senior international competition, and won the event ahead of former European Champion Júlia Sebestyén. At the 2007 U.S. Championships, she placed 13th.
In the 2007–08 season, Williams-Stewart was assigned to another senior international competition, the Nebelhorn Trophy. There, she won the silver medal behind reigning European Champion Carolina Kostner and ahead of Finnish skater Laura Lepistö, who would go on to win the bronze medal at the 2008 European Championships. At the 2008 U.S. Championships, Williams-Stewart repeated her 13th-place finish of the previous year.
Following the 2007–08 season, Williams-Stewart switched to compete representing Puerto Rico. She was released by the U.S. Figure Skating Association in the summer of 2008 and began representing Puerto Rico in club competitions over the summer.