Short answers, pulled from the story.
Constanze Mozart, born Maria Constanze Cacilia Josepha Johanna Aloysia Weber on the 5th of January 1762, was an Austrian soprano and the wife of composer Wolfgang Amadeus Mozart. She is known both for her nine-year marriage to Mozart and for her role after his 1791 death in publishing his works, organizing memorial concerts, and shaping his posthumous reputation.
Constanze and Wolfgang Amadeus Mozart married on the 4th of August 1782 in a side chapel of St. Stephen's Cathedral in Vienna. The marriage took place under urgent circumstances, and Leopold Mozart's written consent arrived by mail the following day.
After Mozart died in 1791 leaving debts, Constanze secured a pension from the emperor, organized profitable memorial concerts, and campaigned to publish her husband's works. She also collaborated on the first full-length biography of Mozart with Franz Xaver Niemetschek, and later published a second biography with her second husband, Georg Nikolaus von Nissen, in 1828.
Constanze sang in the 1783 premiere of Mozart's Great Mass in C minor in Salzburg, and the demanding soprano solos in that work were written for her voice. She also directly prompted Mozart to compose fugues, including the Fantasy and Fugue K. 394, after she heard works by Bach and Handel at the home of Baron Gottfried van Swieten and, as Mozart wrote to his sister Nannerl, "absolutely fell in love with them."
Constanze Mozart's second husband was Georg Nikolaus von Nissen, a Danish diplomat and writer who initially rented a room from her. They began living together in September 1798 and married in 1809 in Pressburg, today's Bratislava, because a Catholic-Protestant marriage was not legally permitted in Austria at the time. Nissen died in 1826, two years before Constanze published the Mozart biography they had worked on together.
According to the Grove Dictionary of Music and Musicians, early twentieth-century scholarship severely criticized Constanze as unintelligent, unmusical, and unfaithful, calling her a neglectful and unworthy wife. The Grove Dictionary concludes those assessments were based on no good evidence, were tainted with anti-feminism, and were probably wrong on all counts. Modern Mozart biographies by Braunbehrens (1990), Solomon (1995), and Halliwell (1998) also raised complaints about unfair treatment of Constanze.