Complex sentence: O'Reilly was so indispensable to the bureau's operations that President Franklin Delano Roosevelt postponed her retirement, scheduled for 1935, to 1938, after she had worked at the Mint for a total of 34 years.
Split into simpler sentences: O'Reilly was so indispensable to the bureau's operations that President Franklin Delano Roosevelt postponed her retirement, scheduled for 1935, to 1938. Upon her retirement, she had worked at the Mint for a total of 34 years.