Dorothy Walker Bush Koch , often called `` Doro , '' ( born August 18 , 1959 in Texas ) , is the daughter of the 41st President of the United States George H. W. Bush and former First Lady of the United States Barbara Bush . Dorothy Walker Bush Koch , often called `` Doro '' , ( born August 18 , 1959 ) , is the daughter of the 41st President of the United States George H. W. Bush and former First Lady Barbara Bush , and the youngest sibling of George W. Bush , the 43rd President .