From the Super Mario Wiki
Constanze Mozart (née Weber) was the wife of composer Wolfgang Amadeus Mozart. The two married on August 4, 1782 after Wolfgang spent some years courting her and after he had been rejected by Constanze's sister, Aloysia Weber. The two stayed married until Wolfgang's death in 1791 and had six children together, notably Karl Thomas Mozart (written in-game as Carl) and Franz Xaver Wolfgang Mozart. In Mario's Time Machine, she meets Mario after he travels back in time to Vienna in 1791 to bring a Flute to Wolfgang after it was taken by a time-traveling Bowser.
Mario's Time Machine
According to Mario's Time Machine, Constanze Mozart lived in Vienna circa 1791 with Wolfgang and her children. When Mario first speaks to her, he asks her if she knows Wolfgang Amadeus Mozart. She then says that she is, in fact, his husband and asks if Mario is attempting to collect a debt from them. Mario refutes this and asks her if she owes money to a lot of people. She replies that since the two of them have no steady income, their finances are constantly fluctuating. She also calls her husband "Wolfie", which she says is her pet name for him (despite this being a detail from the heavily fictionalized film based on Wolfgang's life, Amadeus). She also mentions how Wolfgang was initially pursuing her sister, Aloysia, before deciding that he was better off with herself. Mario comments that their relationship seems nice, but he is worried about their lack of income. Constanze agrees, but she brings up that while most people enjoy her husband's music, the aristocracy does not care for it, and only pays him with baubles and trinkets. To prove her point, she gives Mario one of the Buckles that was given to him as payment. She also mentions, however, that a rich person has recently been interested in commissioning an opera from Wolfgang. She then excuses herself as she looks for Carl's toy. Mario promptly gives her the Toy that he received from the Mozarts' friend, Joseph Haydn. Constanze thanks Mario and invites him to join her and Wolfgang for Haydn's farewell dinner. She also says that Haydn often taught Wolfgang, to the point where Wolfgang considers Haydn to be a surrogate father. Mario realizes that Wolfgang's actual father has passed away and apologizes, and Constanze appreciates the sentiment. She mentions how his father, Leopold Mozart, taught him music and took him and his sister, Nannerl, to see various concerts. Mario comments that Wolfgang is talented, but Constanze also assures him that he relies on hard work and inspiration, and right now, he needs to find some inspiration. Mario then pulls out his Flute, wondering if it might inspire him, and Constanze says that's a wonderful idea and tells him to bring it to him immediately.