Actress Lindsay Lohan, working to rebuild her acting career after a year of personal turmoil, will appear as a guest star on the ABC television comedy "Ugly Betty," the network said on Monday.Lohan, who has not starred in a feature film since last year's flop "I Know Who Killed Me," will join the popular sitcom's cast for six episodes, playing a mean former classmate of title character Betty, who suddenly resurfaces in her life.