Complex sentence: In 1992 she was awarded the National Medal of Science which is the highest scientific honor in the US and is rarely awarded to psychologists as there have only ever been 5 awarded at the time.
Split into simpler sentences: In 1992 she was awarded the National Medal of Science, which is the highest scientific honor in the United States. This award is rarely awarded to psychologists as there have only ever been 5 awarded at the time.