MOUNT VERNON, Mo. — Southern gospel music singer and songwriter Dottie Rambo, 74, was killed when her tour bus ran off a highway near Mount Vernon, Mo., May 11. She was en route to an engagement in Texas after performing in Illinois. Born Joyce Reba Luttrell in Anton, Ky., Rambo wrote more than 2,500 songs, including "We Shall Behold Him,"…