Clara Harris was the fiancé and murder victim of Major Henry Rathbone. Clara Harris was with Rathbone while he accompanied President Abraham Lincoln when Lincoln was shot during a production of Our American Cousin at Ford's Theatre.
In the Timeless Universe
In the original timeline, Henry Rathbone accompanies President Abraham Lincoln and First Lady Mary Todd Lincoln along with his fiancée, Clara Harris on April 14, 1865. After John Wilkes Booth shoots Lincoln, Rathbone tries to stop him but is non-fatally stabbed in the abdomen.
In the altered timeline, Rathbone does not accompany Lincoln or get stabbed. Clara Harris doesn't go to the play either. Instead, Ulysses S. Grant and Robert Todd Lincoln watch the play with the president.
Clara Harris at Wikipedia