On 18 August 1765, Francis I, Holy Roman Emperor died. The fifty-six-year-old Emperor who was in good health at the time and he had been in Innsbruck with his court celebrating the marriage of his son Leopold. Francis had suffered a slight seizure on 17 August but he felt better the next day. He collapsed as he walked back to the palace after a theatre performance. He was carried into the anteroom but by then he was already dead.
Francis was succeeded as Emperor by his son Joseph II, with Peter Leopold, his younger son, succeeding as Grand Duke of Tuscany. Francis’s widow, Maria Theresa, mourned his death deeply. Maria Theresa gave up on wearing anything extravagant or fashionable, wearing only black for the remainder of her life. She also had the rooms of her palaces painted black and would spend the entirety of August in seclusion each year. Her life would never be the same again without her husband; Maria Theresa said “I hardly know myself now” after losing Francis.
After marrying Francis, Maria Theresa had made her husband co-ruler of her Habsburg lands, which included Austria, Hungary and Bohemia, among others. Despite always being the main ruler over her vast dominions, Maria Theresa felt the need for the support of a co-ruler again after the passing of her husband and elevated her son Joseph to the position of co-regent over her lands. Mother and son did not always agree on matters of politics and governance, causing Joseph to threaten to step down on a number of occasions, the working relationship between the pair was always difficult.
Sounds to me as if Maria Theresa developed a mental disorder. Depression in reaction to grief lasts 6 months to a year and is considered normal. Grief that persists for longer, particularly a lifetime as in Maria Theresa case is abnormal and often is due to a psychotic depression.