Simplify the following text for a Grade 4 native English-speaking person.
Original: Upon F.D.R. 's death on April 12 , 1945 , Harry Truman took the presidential oath of office and Bess Truman became the new First Lady .
Simplified: Many persons call her by another name , Bess Truman or Bessie Truman . She was the First Lady of the United States from 1945 to 1953 .