Short answers, pulled from the story.
Aloysia Weber (c. 1760 - the 8th of June 1839) was a German soprano who sang at major Viennese theaters and was the sister-in-law of Wolfgang Amadeus Mozart. She is remembered for her association with Mozart, who fell in love with her, taught her singing, and wrote a substantial body of music specifically for her voice.
Mozart composed numerous works for Aloysia, including the recitative and aria K. 294 "Alcandro, lo confesso," the aria K. 316 "Popoli di Tessaglia" (noted for reaching the highest demanded note in the classical repertoire), K. 383, K. 416, K. 538, and two substitution arias (K. 418 and K. 419) inserted into a Burgtheater revival of an opera by Pasquale Anfossi in June 1783. He also wrote the role of Madame Herz in Der Schauspieldirektor K. 486 for her.
Aloysia Weber became Mozart's sister-in-law when he married her younger sister Constanze Weber in 1782. Before that, Mozart had been in love with Aloysia and expressed a desire to marry her, though she did not reciprocate.
Aloysia Weber married Joseph Lange on the 31st of October 1780. Lange was an actor at the Theater am Karntnertor in Vienna and an amateur painter who later produced a well-known portrait of Mozart. As a condition of the marriage, Lange agreed to pay Aloysia's mother 900 florins upfront and 700 florins per year.
Aloysia sang Konstanze in revival productions of Die Entfuhrung aus dem Serail (1783, 1785-1789), Madame Herz in Der Schauspieldirektor at its Vienna premiere in 1786, Donna Anna at the Vienna premiere of Don Giovanni on the 7th of May 1788, and Sesto in performances of La clemenza di Tito in 1794 and 1795.
The Danish actor and musician Joachim-Daniel Preisler, writing in his diary after hearing Aloysia sing privately in Vienna, called her voice "something exceptional" and praised her high range, delicacy, execution, taste, and theoretical knowledge. He also noted she could sing the longest and most difficult parts better than the Italian singers favored by the Viennese nobility, and that she could accompany from a full score and play interludes like a Kapellmeister.