Lines of Communication - S4-E11
Trivia: Marcus tells the Mars resistance fighters that he was raised on the planet Arisia. J. Michael Straczynski used that name as an homage to one of his favorite science fiction book series, E.E. "Doc" Smith's Lensmen novels, in which the Arisians were the good guys. (00:16:00)
Chosen answer: She was promoted to Captain and thus had to leave Babylon 5, becoming a captain on a new Warlock class ship. Later on she retires/quits and becomes the top Ranger on Minbar.