 Following her fiftieth birthday in May 1767 , Maria Theresa contracted smallpox from her daughter @-@ in @-@ law , Maria Josepha of Bavaria . She survived , but the new empress did not . Maria Theresa then forced her daughter , Archduchess Maria Josepha , to pray with her in the Imperial Crypt next to the unsealed tomb of Empress Maria Josepha . The Archduchess started showing smallpox rash two days after visiting the crypt and soon died . Maria Carolina was to replace her as the pre @-@ determined bride of King Ferdinand IV of Naples . Maria Theresa blamed herself for her daughter 's death for the rest of her life because , at the time , the concept of an extended incubation period was largely unknown and it was believed that Maria Josepha had caught smallpox from the body of the late empress . 
