Ryan most recently served as inspector general of the Smithsonian Institution, where she led an independent office that conducts performance audits and investigates crimes relating to the organization's programs and operations.

At Berkeley, Ryan was editor-in-chief of the Ecology Law Quarterly. After graduating from Boalt Hall, she clerked for Judge Joyce Hens Green of the U.S. District Court for the District of Columbia. She then practiced with the law firm Beveridge & Diamond in Washington, D.C. In 1995 she joined the Environmental Crimes Section of the U.S. Department of Justice as a trial attorney, and during that time served as a special assistant U.S. attorney with the U.S. Attorney's Office for the District of Columbia. In 2000 she became an adjunct professor of law at the College of William & Mary, where she taught a course in legal skills and ethics, advanced brief writing and a seminar on the Electoral College.

Ryan joined the Smithsonian's Office of the Inspector General as counsel in 2003, became assistant inspector general for investigations in 2005, and in 2007 was named inspector general.