Complex sentence: She started her career as an illustrator while working for the Department of Agriculture and after leaving the USDA in 1969 worked as a resident illustrator for the Smithsonian Institution until 1990.
Split into simpler sentences: She started her career as an illustrator while working for the Department of Agriculture. After leaving the USDA in 1969 worked as a resident illustrator for the Smithsonian Institution until 1990.