Jill Biden would scramble into cocktail dresses in a bathroom at Northern Virginia Community College before rushing to White House receptions when her husband was vice president. She graded papers at night in a tiny nook on Air Force Two. Her Secret Service agents dressed like college students and carried backpacks to blend in when she was on campus. Now “Dr. B,” as her students call her, plans to continue teaching English and writing at the college when she moves into the White House in January. She will be the first president’s wife to continue her professional career as first lady, after becoming the first second lady to do so. She will also be part of a small group of union members to hold the title, including Eleanor Roosevelt and Nancy Reagan.