Princess Isabella of Parma

Born in 1741 to the Duke of Parma and a French princess, Isabella grew up lonely under demanding caretakers, losing her mother young. At 18 she married Archduke Joseph of Austria, heir to the Habsburg throne, but couldn't return his devotion — her heart belonged to his sister, Archduchess Maria Christina, a bond likely romantic and a source of crushing guilt she deemed sinful. In private she wrote prolifically: essays arguing for women's intellectual equality, treatises on military theory, diplomacy, education, religion. Nineteen works survived; none saw print while she lived. Four pregnancies…