Long's acting coach was Betty Bridges, better known as the mother of Diff'rent Strokes star Todd Bridges. Her earliest role was in the Disney television movie, The B. R. A. T. Patrol alongside Sean Astin, Tim Thomerson and Brian Keith. Her first notable role on television was a three-year contract role as Kathryn "Kat" Speakes on the soap opera Guiding Light. Long portrayed Kat from 1991 to 1994. Long played Brandi in Boyz n the Hood. The film excited Long, who was doing her "first real movie role". It helped Long build her confidence as an actress. "It introduced me to the world in a way that it was okay for me to be who I am and still find success," she added. "I didn’t have to conform to anything. " From 1994 – 1995, she played Will Smith's girlfriend and fiancée Beulah "Lisa" Wilkes on The Fresh Prince of Bel-Air. Jada Pinkett Smith was originally supposed to play Lisa, but was too short for the role (opposite a 6'2" Will Smith), thus leaving Nia to take the part.