Vaughn turned professional in the 1998 season and her first year was her most successful. She achieved a 100 m hurdles best of 12.63 seconds in July at the U.S. Open Track and Field and was runner-up at the 1998 USA Outdoor Track and Field Championships behind Cheryl Dickey. There was no Olympics or World Championships in Athletics held that year, but she performed well in other international competitions. On the 1998 IAAF Golden League circuit she won at the Golden Gala in Rome, narrowly beating fellow American Melissa Morrison-Howard. She was the gold medallist at the 1998 Goodwill Games and a silver medallist for the United States at the 1998 IAAF World Cup, finishing behind Glory Alozie of Nigeria. She was down in eighth at the close-of-season 1998 IAAF Grand Prix Final.